First...BABIP:
Garko's seen his BABIP drop in each successive season from 2006 to 2009...and I can find no obvious statistical reason why this should be the case.  Either the league is booking him, or he was just lucky the first couple of years and it will even out to around the .300 MLB average.
Second...Trajectories:
I see no trend in his grounders or flyballs or even his HR/Fly (though he was a little unlucky in 2008 in that regard).  I see a steady climb in LD% that would have continued in 2009 prior to his move to the NL.  He's hitting the ball either harder or at least on a more level plane.  The result should be an increasing BABIP, but we have not observed this.  In part because he's hit into an INSANE number of infield pop-ups the last two years (BABIP of nearly zero).  All statistical evidence suggests that there is essentially no correlation between pop-ups and any other skill or between  pop-ups in one season and the next.  It's possible that Garko, while working on his batting eye, is just hitting into some weird outs...but I don't see that continuing.  Either, he gets "well" at the plate and starts attacking with gusto again...or he doesn't, and the pop-ups still go away when he goes to his pepper swing.  Either way, he doesn't stirke out much at all and we should expect him to have a good solid .280 average and .300 BABIP given normal luck.
Third...Eye:
As Doc notes, his batting eye is rapidly improving...a trend that continued even in the NL.  Not only is his K/BB droping (from 3-ish to less than 2), but his P/PA haven't changed - implying that he was always patient (running P/PA wel over 4.00 for his whole career in the bigs) but now he's converting that into real results (ignoring the weirdly low P/PA he had in '09 which was likely an outlier).  It seems the main reason, however, for the decreased K rate and K/BB is an increase in contact percentage.  His SW% and O-SW% are essentially steady, so it's not that he's getting smarter up there...just better at making contact.  Still, the guy is not Jose Lopez...he works the count very well, a la Franklin Gutierrez, and we all know Zduriencik loves this type of player.

I think given his so-so hitting vs RHP and lack of secondary skills and defense, I'd just keep him as a platoon player. I DO like him in that role though.
Something that needs to be touched that isn't getting a lot of play is that the Ms are going to be worse against RHP than they were last year. Branyan over Kotchman might solve a bit of that, but right now we are very strong vs LHP and very weak vs RHP. The team offense IS NOT built to the park.

Lopez, Gutierrez, Ichiro, Moore/Bard/Johnson and Wilson don't have much of a platoon split...so we're not THAT much worse against the righties...
It would be nice to upgrade one left handed bat...but I don't think it's all that huge an issue...we might be weak against right handed ground ball pitchers though since a lot of our hitters who fair decently against the right handers are groundball hitters.

Gutierrez and Wilson have really wide platoon splits. The C tandem will likely have one as well.
Lopez and Ichiro don't have much of a split.
We're better against LHP than RHP at EVERY single position either than 3B.
We need a hitter at 1B at the very least that can mash RHP, preferrable one thats strong vs Groundball pitchers... I think I can come up with one that would cost the same as Kotchman. :-)

People need to stop looking at a player's splits, at least for righty batters, because it tells you practically NOTHING about his ability to hit lefties. Even if a right-handed batter has 2000 PA's against lefties (not total PA's, just versus southpaws) you still need to regress his split 50% towards the league average. So very few right-handers play enough in their careers that you can take their numbers against lefties at face value. Therefore, you are better off looking at the guy's total performance and assuming a normal split.
(The number of PA's against lefties [again, emphasis on lefties] needed to regress splits half-way for other players is as follows: lefty batters- 1000, switch-hitters-600, righty pitchers- 700, lefty pitchers- 450)
Matt, could you come up with a simple split calculator where you put in a guys batting line and it spits out what his expected righty/lefty numbers would be? I'm not even talking about doing any regression, just assuming a league average split.

I'm not buying it for some of these guys with longer career track records like Ichiro, J. Wilson, Lopez, Byrnes and Bradley.
Some guys have wider splits than others, some have none, some rare guys like Ichiro have opposite hand splits. Granted with a low sample I understand regressing the splits a bit (and even then most of these players are still going to be higher than average), but after a while a guy is what he is.
The '10 Mariners are going to be much stronger vs LHP next season.

...the average platoon split for a right handed batters is 15 points of wOBA...that's not exactly OPS...and there's no direct way to convert wOBA into an estimate of the OPS split...but let's assume for the sake of argument that all Mariner hitters actually have league average platoon splits and face a league average percentage of lefty and righty pitchers (we know the second part is not true, but go with it here)...LHP get about 29.6% of the total plate appearances per B-Ref, so a 15 point wOBA split would be achieved by taking the batter's total wOBA, moving his vs. RHP wOBA down by 0.015*0.30 (about 0.005) and moving his vs. LHP wOBA up by 0.010.
Lopez' wOBA in 2009 was .325, so you'd expect him to hit .320 against righties and .335 against lefties.
Interestingly, the average split for a left handed batter is about 0.030 points of wOBA...twice as much.  Probably because they don't get to face their weak side very often.  Ken Griffey Jr. wOBA'd .323 last year...you would expect him to wOBA .303 against lefties and .333 against righties.
Let's now assume that Ichiro, Figgins, Lopez and Bradley - all of whom have established that they don't have normal platoon splits (two of whom switch hit so you expect the splits to be muted anyway) have no platoon split, and let's assume the rest behave normally.
Projected wOBA vs. LHP:
RF) Ichiro! .355
3B) Figgins .345
DH) Bradley .370
1B) Garko .355
CF) Gutierrez ..345
2B) Lopez .335
C) Catchers .310
SS) Wilson .305
LF) Byrnes .325
Projected wOBA vs. RHP:
RF) .Ichiro! .355
3B) Figgins .345
LF) Bradley .370
CF) Gutierrez .330
DH) Griffey .335
2B) Lopez .320
1B) Kotchman .340
C) Catchers .295
SS) WIlson .290
So yes...the line-up vs. RP is weaker...but we're not looking at a major disaster on our hands...just...a potential weakness.

I can see the logic in regressing players without a suitable # of PAs.
That said, I have some problems with using a blanket rule on a pool of players to evaluate an individual player's skill set. You might as well regress Ichiro and Figgins to a .300 BABIP. Our team is full of players whose splits are anything but normal, and many of them have been around for a while now.
I do think this team will be at least 40 OPS points stronger vs LHP come June. The only regular whos consistently stronger vs RHP is Figgins. 

Of the guys you list, I am not saying they should all be treated the same, only the right-handers. Ichiro is lefty who has faced southpaws nearly 2000 times so you can take his splits at face value, and Bradley is switch-hitter so you have to look at his splits to determine his strengths (since some switch-hitters are natural righties and others natural lefties, there are going to be big differences amongst them).
"but after a while a guy is what he is."
Right, but the vast majority of righty hitters are the same and it takes a long, long time before you can know who don't fit the mold, far longer than anybody seems to realize.
"The '10 Mariners are going to be much stronger vs LHP next season."
Note: I'm not arguing this. I am just trying to make a general point about the value of splits.

[Please take it easy, guys]

against RHP.  CF/RF/SS/2B/C are going to be neutral, being the same players that were there last year, 3B gets better, 1B gets worse to a very similar extent, DH gets better, and LF stays the same or gets slightly better (it would be hard for it to be much worse than last year).  Certainly they didn't improve by leaps and bounds, but I think it's hard to say they're worse.

Branyan by himself had a 1.100 OPS vs groundball pitchers. Ichiro had a strong year vs Righties, Lopez had 21 HRs vs RHs, Rob Johnson was better vs RH by 200 OPS points thank to a BABIP flukish split. Hannahan, Chavez, Cedeno, Johjima, Wlad and Sweeney ALL hit better vs RHs. We got a very flukishly stonger line vs RH last season.
The only regulars who were stronger vs LHP last season were Gut and Griffey. Beltre and Betancourt didn't get enough ABs to make a difference.
I don't think we'll be significanltly worse vs RHP next season, but GB righties in particular are going to be a bad matchup.
The production vs LHs (and filling holes) will make us a better overall offensive team. Its just pretty unbalanced right now and not fitting to the park.

Methinks the problem here is that there is a tendency to speak about EITHER park effects of Safeco *OR* handedness splits.  The reality is that both are in play 81 games a season.
If the team is set up to be better against LHP --- SAFECO, by itself -- sets it up to be better against RHP.  When a righty pitcher takes the mound in the Safe, all those switchers turn around, and get to aim at the "easy" HRs, instead of fighting against the die-at-the-track effect of LF.
In Safeco, the opposition WANTS to start LHPs, because right-hand bats don't fare well.  So, what do you need in Safeco against LHP?  You need right handed bats with superior power against LHP. 
The biggest difference between '09 and '10 that I see on the horizon is that Wak will actually have a bench that he can use both strategically and tactically.  The THREAT of the lefty-killer on the bench makes bringing in the LOOGY a much dicier move -- drastically so compared to the Cedeno/Wlad/Sweeney bench of much of '09.  And, of course, the same rules apply in any road parks with short rights or deep lefts.

Sandy, what an incisive couple of paragraphs!
How cool is that: get your opponents to disarm themselves of their best weapons.
Kind of like the great cornerback who never gets any intereceptions because no one ever throws it over there, it'd be hard to fully capture with stats.  Gotta stat for how many times the dog doesn't bark?

Wasn't intending to recommend - just analyze.  I don't believe there is ONE best way that works better than others.  I just think there is a (unavoidable?) reality that the more focused on details one gets - in any endeavor - the easier it becomes to lose track of the big picture.
In American business, when the GOAL becomes: making money -- or cutting expenses -- or increasing market share -- the potential pitfal is to forget to pay attention to the product or service being provided - and when that happens .... CRUNCH!
This isn't to say that any and all of the details aren't important.  They are.  But, the quality orgs (baseball or not), are those that keep track of BOTH the 30,000 foot view and can grab the microscope, too. 
I chuckle over the angst of the whole Kotchman, Garko, Langerhans, Byrnes, Carp, Tui, (Endy?) situation around the web.  The reality is the club isn't locked into *ANY* specific choice today.  They get to make those choices at the end of ST.  But, all in all, I see the club going into ST in 2010 in a VASTLY superior situation (offensively) than they did in '09.  And I don't see ANY of the "who is gonna be" candidates being a lock-down can't-dump-due-to-dollars situation.  All things being equal, yeah, the 4 million man will stick over the 400k man.  But, if all things are NOT equal - I see lots of room for juggling.
I think many have forgotten that 2009 began with Tui taking Ichiro's roster spot for the first two weeks of the season, (and never getting to play).  I think it has been soooo long since the club had a decent bench, many just have no concept of what a difference a quality bench can make.  Between the no talent benches - plus the veteran entitlement, why should anyone understand?
In 2009, the club had roughly 1400 PAs from non-ST bodies.  Most were a result of emergency surgery.  Many of the bench bats failed so miserably, (Wlad, Cedeno, Jack Wilson), that getting an 80 OPS+ out of a bench guy was seen as major progress. 
I see a 2010 ST roster that has the 'potential' to produce 6 100 OPS+ positions, with a 7th, if things break well.  They had 4.5 players at that level in '09 -- and if this roster produces 6 full-time 100 OPS+ producing POSITIONS - (even if by way of platoon), then the offense will improve, Branyan or not.  Getting CA, SS and LF out of the 60s up into the 80s is 3 times as critical as dropping from Branyan's 128 to Kot/Gar/Car's 100. 

#1 is Kotchman and #2, obviously, is . . .
Kotchman
I'm with Sandy.  It's kind of silly season on the web, but Z seems to have a lot of the picture in focus.  Get better without disastrous contracts, giving up too much flexibility or blocking anyone too important.
Which role player Wak orders off the menu is not as important as the fact that the menu seems to have been put together in a savvy manner.

I don't remember the exact details but I believe he was traded for Hall and a prospect with limited cash changing hands to cover their salary differences.  Even though Kotchman's salary will be about $3.5m, a big chunk of that is being paid by Milwaukee.
Regardless of the exact details, my point is that the Ms investment in Kotchman is actually minimal and if he busts they can drop him easily.  That said, it sounds like it is his job to lose.

This is true for relievers, although teams aren't going to switch up their starting rotations.
Is this really an advantage though? I don't want teams throwing out their RHPs at Safeco against our offense.
At the same time you make a good point about the switch hitters having less of a penalty vs RHP. Even so, the strongest park of our offense is geared towards the worst part to hit in our park.
It is likely that SAFECO will help shrink these stats 10 OPS closer together, but we're still going to need those lefties in Safeco.
Its a GOOD thing the Ms are strong vs LHP, I just thought it was interesting that for all the talk of building to the park this team isn't far off from the Bavasi teams stylistically. Its stronger vs LHP, and not a single bat in our lineup has a platoon advantage against RHP either Figgins.

Y'know -- in scanning the career numbers for these three, I see an eerie similar pattern.  Each has managed at least one AMERICAN LEAGUE .800 OPS season, (Kotch and Garko both broke .840, while Byrnes peaked at .810.
All three have also have MASSIVE dips in performance along the way - including limited exposure outings below .650.  Oddly, all three have career totals that are higher when playing in the AL?!?  All three have shown a staggering ability to LOSE their job.
It's like three rolls of the dice at a .280/.350/.450 bat.  Clearly, Garko has the best resume, but he's two years older than Kotchman, (but the two have nearly identical PAs).  Byrnes is the old man of the bunch.  I'm thinking Kotch is the front-runner for PT, not because of his salary, but because he's a lefty bat for Safeco. 
The aggregate 1B bat in 2009 was .848.  How significant IS a downgrade from .850 to .810, (if .810 is what you get out of the 1B mish-mosh)?  That's a 5% dip in performance in 9% of PAs?  Maybe you only get .770 from the mix -- a fulll 80 point (10%) decline.  How many runs does that REALLY cost? 
Frankly, Figgins posting a .750 at 3B would MORE than off-set the dip from Branyan.  (Third totaled a combined .643).  So, Figgins/mish-mosh by itself off-sets Beltre/Branyan.  That's BEFORE you even look at the .597 from short -- or the .609 in LF. 
So, I will continue beating my -- it ain't the BIG bat that is critical -- it's avoiding the multiple mini-bats ... the 3 (or more) 60-something OPS+ guys -- who shorten games and steal PAs from guys like Ichiro. 
Year one:  Fix the defense.   Year two:  Fix the OBP.  Year three?  That's when you can look at the power shortage ... so long as you haven't AIGed your payroll already.

I agree with you that the 1B platoon isn't a disaster. Its probably worth 1-1.5 WAR. The problem is you're burning two roster spots for that production and paying $4mil for it (not really a value deal). Since Kothman is making the money and Garko is only making 550K gauranteed, the real problem is Kotchman.
Kotchman would have been fine at the MLB minimum like Garko or Byrnes, but hes making $3.5mil. I actually think Byrnes is potentially the best player of the three and since you can leverage his large platoon splits hes a really nice #4 outfielder.
Overall the Kotchman move isn't that big of a deal in the big picture. It just sticks out as a big question mark and waste of resources in an offseason that so far has been brilliant.

The 3.5 mil we're paying Kotchmannis all on us.  The money we got from Milwaukee to cover Hall all went to Boston.