There was a time when Bay was a much better player than Figgins. It just doesn't look like thats the case anymore. Bay is still an excellent hitter, but has declined significanly defensively in LF over the past 3 years, and hes probably not that far off from becoming a DH-only type.
Figgins, on the other hand, has turned into a tremendous defensive 3B and has polished his plate skills over the past two years. He led the AL in OOZ plays at 3B and was #1 in PMR in '08.
Guess who also tied Franklin Gutierrez for the most defensive runs saved according to Bill James' plus minus? Gutierrez and Figgins tied at 31 runs saved in '09.
I remember when we traded for Gut in the first place and the argument against him being a historically great defender was essentially "nobody is this good". This was despite the fact that we had all sorts of data that Gut PERFORMED as a +20-30 run full-time RF over the past two years. 
Over the past two years theres a lot of evidence that Figgins is one of the elite defending 3Bs in baseball. I'm thinking that Z is probably buying into Figgins' improvement as well. I'd bet on a 4-4.5 WAR season for Figgins in '10 (with a +10-15 run glove at 3B). We can get our offense at 1b and DH a LOT cheaper with something like Branyan + Thome.

Personally, I put zero, zilch, nada weight on individual defensive stats coming out of Boston's LF.  Some historical perspective.  Looking at only the range portion of UZR.
Manny:
2002 - (1.8)
2003 - +3.7
2004 - (0.8)
2005 - (19.8)
2006 - (20.6)
2007 - (21.0)
2008 - (5.7) - combined from Boston/Dodgers
2009 - (2.9)
According to UZR, between 2004 and 2005, Manny lost 20 runs of range, which he maintained right up until the instant he was traded, at which point, he got back 17 of those runs.
As a comparison, let's look at his RF/9 over the same span.
2002 - 1.7
2003 - 1.8
2004 - 1.7
2005 - 1.9
2006 - 1.6
2007 - 1.7
2008 - 1.8
2009 - 1.6
It just so happens, that 2005, the year Manny morphed into the worst fielder in baseball, he set his CAREER HIGH in actual putouts, (243).  UZR gave him a 7.0 ARM rating that year, (he had 17 assists, so not shocking). 
Jason Bay was a plus fielder until 2007, (by UZR), then plunged toward Manny-land, with -14.6 and -14.4 range ratings since arriving in Fenway.  Note that while Manny was posting consistent 1.7ish numbers, Bay posted a 1.8 in his first partial season in Boston, but posted a 2.3 RF/9 in 2009, and made 310 putouts, (and added 15 assists).  Somehow, UZR says Bay COST the team 0.7 runs with his arm.
How many LFs in all of baseball posted a 2.3 RF/9 in LF?  Three -- Crawford, DeJesus and Bay.  To believe that Bay is *HORRID* in LF, I have to believe that a RF VASTLY above that of any LF in baseball would be required for him to be AVERAGE.  Bay records the 2nd most outs of any LF in baseball, (trailing only Crawford), and is pegged as a bumbling bafoon by UZR. 
Sorry, but if UZR says Manny was an average LF in 2004 with 198 POs, a 1.7 RF/9 ... and then contends Bay, with 310 POs, a 2.3 RF/9 in 2009 cost them more than 14 runs due to his poor range ... well, then UZR is a complete moron.  (Or is anyone who chooses to believe UZR in this case). 
According to Fangraphs, Bay was "expected" to make 327 outs.  That would make him (in theory), a perfectly average LF.  That was the most outs made by ANY LF in all of baseball.  I am supposed to believe that Boston has what ... an order of magnitude more chances for the LF than any other LF in all of baseball?  With the GREEN MONSTER?!?!?  In what Bizarro world does LF in Boston become the place to pad DEFENSIVE stats?  You have to go back to 1986 with Jim Rice to find a LF who had more POs for Boston than Bay. 
Manny, at age 38, improves his range runs by 18 by leaving Boston.  I'm thinking Bay -- going to Seattle -- probably ups his range runs by about 60.  (No, that's not hyperbole ... that's my opinion on how reliable UZR range factors happen to be).
 

You do realize Bay was in PITTSBURG for one and a half years since '07 right?
It aint just UZR. PMR and RZR both think hes been awful SINCE 2007. If ONE stat is inconsistent its one thing, when they are ALL saying the same thing?
You're solely using his '09 RF to cling onto the idea that Bay is somehow not a poor fielder. Do you realize that a year earlier (2008) RF had Bay at MINUS 30 runs in LF? And yes most of that was in Pittsburg.
Personally I hope the Angels sign his overrated ass.

Fangraphs isn't arguing against bat-first players. They are merely trying to figure out overall value. Do they rely too much on UZR? I'd say yes, but that isn't neccesarilly the point here.
For YEARS OBP and SLG was an underrated asset in MLB. We've come full circle. GMs are now overpaying for HRs. Defense and baserunning are becoming underrated.
The key is in figuring out a guy's overall value. Offense is still the most valuable asset, but its important to calculate those other factors to figure out what a guy is really worth.

Honestly, the Pittsburgh stats make perfect sense to me.  In 2006, he had 316 POs in 1373 innings, (2.1 RF/9), and a 316 PO versus 307 expected out comp.  UZR had his range at plus 3.3.  I can buy that.
By 2007, the righting was on the wall that Pitt wasn't going to be getting better while Bay was with the team.  The 2007 season, Bay likely played hurt for much of the season, (it was BY FAR), his worst offensive season, also.
In the end, he made 265 POs in 1237 innings, (2.0 RF/9).  Per FG, he should've made 280 outs, but only managed 265.  So, his -8.9 range factor isn't outrageous.  But, he WAS slowed by injury for some of the year -- and he likely also went thru the motions for much of the year.  His career high 8 errors supports that 2007 was a bad year in EVERY aspect of his game.
In 2008, he managed only 254 POs in 1344 combined innings.  That *IS* a very poor showing, (and a personal worst 1.8 RF/9).  By 2008, he just wanted out of Pirate purgatory, and simply concentrated on hitting -- and likely became Ichiro-like in LF, not wanting to risk an injury costing him a chance to move somewhere.  And he did move -- into the park with perhaps the hardest LF in the world to play.  If there's any LF on the planet I would expect a learning curve, it would be Fenway.  He also managed only 8 assists in 2008, (his career worst for 150+ game season).  So, the combo of his lowest outs - his fewest assists since 2005 ... and yes, his 2008 UZR can be defended.
My point is that the 2009 UZR *CANNOT POSSIBLY BE DEFENDED*.  He made 310 POs in 1279 innings -- setting a personal best in RF/9.  He had a career high 15 assists.  He had a career best ZERO errors.  Okay, I can appreciate that if you have a weak arm, teams will run on you, so often the best arms have low assist totals.  But, Bay led the majors with 15 assists from LF, and cost his team 0.7 runs ... while DeJesus threw out 13, and saved his team 6.7. 
My problem with UZR, is that it say Bay *should have* made 25 more outs than any other LF in all of baseball.  Carlos Lee, for the Astros, played only 7 innings less than Bay.  According to this system, in Houston, the "expected" outs was only 217.  In Boston, 327.  I am supposed to believe that somehow, in Boston, there were 120 more "gettable" balls in LF than in Houston.
In looking just at the Boston 2008 stats: Manny had 99 POs in 537.2 innings, (1.8 RF/9), while Bay was just as bad (76 POs in 432.1 innings (1.7 RF/9).  Yet, Manny was pegged at only -3.0 runs, while Bay was pegged at -8.8 range runs cost.  Their RF values are really, really close - (and both significantly behind Ellsbury).  But, Manny, who had 116 more innings cost the team half as many runs via range?!?.  Manny's 6 assists in his 66 games netted him a 4.5 arm, while Bay's 5 assists in 49 games got him 0.4.
It just doesn't track.  I don't believe there is some cosmic field surrounding Jason Bay that causes an exponentially larger number of balls to be hit in his direction that would be catchable by an average LF. 
What I believe is that Bay "gave up" in Pittsburgh, and his poor range ratings are supported by his poor PO numbers.  I believe in 2009, in Boston, his defensive results improved dramatically, (playing for a contender often has that effect), and his raw countables jumped drasitcally.  But, UZR and RZR don't show that.  Why?  Because *ZR* is the problem.  It's the foundation block for most of these stats - and if ZR is wrong, every variation of it is wrong.
Bay jumped from 254 outs in 1345 innings to 310 outs in 1279 innings, and UZR said his range improved from -14.6 to -14.4.  That's 56 extra outs in 66 fewer innings.  Think about that for a minute.  In 7 FEWER games, he netted more than two complete perfect games worth of outs.  UZR is suggesting that to be AVERAGE for Boston in 2009, a LF would've needed to have roughly a 2.5 RF.  In the past 5 years, Carl Crawford is the only LF in all of baseball to post a 2.5 RF. 
You go back to 2005, when Manny only managed 243 POs in LF (1225 innings - 147 games), I can at least entertain the notion that Crawford, (in similar innings), who had 341 POs, was really 35 runs better than Manny in range.  341 POs to 243 POs ... in similar innings.  Yes, I can accept that there could be a major difference in run prevention.
But Bay, in 2009, was second only to Crawford in putouts, had a basically identical RF/9, and they played the same innings, (3 apart).  I CANNOT accept that the 17 extra POs Crawford managed in 2009 explain the 32 run differential in range rating from UZR.  It makes no logical sense.

Many total putouts are a good measure of defensive value. Sometimes they aren't. A certain fielder could have 20 more "routine" plays than another in a certain year. It happens all the time and is part of the reason D stats fluctuate so much.
RF is the ONLY stat that liked Bay in '09 and it HATED him in '08. 3-4 DIFFERENT systems rate him as a poor fielder from '07-'09. Theres just very little evidence that Bay is still a league average fielder.

Well, raw POs liked Bay, (2nd in the majors).  Raw assists liked Bay, (led the majors).  Raw errors liked Bay (again - led the majors).
If you're going to count every ZR variant, I see no reason not to count POs and RF as different stats.  (Okay, I'm getting snarky here.  Sorry).
I'm not trying to argue that Bay is an elite defender.  I've stated that I think he's average, but could see with his speed, rating as slightly above, given the proper setting and motivation.  My point about *ALL* of the ZR-based stats is that they are all reliant on the initial decisions by the people judging the zones. 
I don't see how one could logically conclude that the smallest LF in all of baseball should produce the most outs of every LF in baseball.  We KNOW from years of data that the Monster creates doubles that would be outs in other parks.  Fenway, should - as a rule - produce fewer out opportunities for ANY LF.  Yet, UZR for 2009 projects Fenway to have produced more expected outs than any other stadium in baseball?!? 
Boston had a bad team defense in 2009.  So, yeah, I can see Bay benefitting from extra chances due to plays not made elsewhere.  So, no.  I don't think he's an elite fielder.  But, I checked Boston stats to see if I could find a Boston team with a similar BABIP allowed.  As luck would have it, the 2006 ane 2009 clubs both gave up .313 BABIPs to the opponent.  So, two teams, more or less identical DERs ... in the same home park.  How did their LFs compare?
The TEAM LF in 2006 -- 274 POs -- 1.81 RF/9. 
The TEAM LF in 2009 -- 365 POs -- 2.27 RF/9. 
It's not that I don't understand that the makeup of a staff can't have an effect on the number of chances a player will get.  I understand this.  What I don't believe, and 40+ years of watching baseball and perusing stats tells me, is that for a position that runs a pretty steady 2.0 ish RF, (2 outs per game), that 100 extra "routine" chances aren't just going to magically appear to skew the results for one guy.  It's the MAGNITUDE of the gap between the outs Bay actually recorded and what the system believes he should have gotten.  I don't believe the system, when the system says you have to set an RF record just to be considered average.  MAYBE, if your team is allowing 100 runs more than everyone else, I'd consider it.  But Boston was 3rd in fewest runs allowed, (yes, they had a good staff).  But, for a team that allowed 35 runs BELOW league average, I'm not buying that Bay and Ellsbury cost them 30 runs more than average.
 
 

Also I'm pretty sure that there are at least 2 different organizations that collect data for their zone ratings, but I'd need someone to check me on that.

In 2009 the Red Sox had the SECOND HIGHEST flyball% (40.9%) in all of baseball. This is why Bay's 09 RF numbers are out of whack. If you go even a year back with RF you can see that they rated him -30 runs in '08.
I'm not saying that Bay is a true minus 30 run outfielder, but his range+arm make him at least a minus 10 run LF, and hes not going to get better with age.
In '06 the Red Sox had a medium flyball percentage at 36.6%.
 

I also don't understand why you keep using RF to argue that Bay is an average fielder. RF dislikes Bay MORE than current metrics, not less. 
RF has Bay as a CAREER -10.56 runs per 150 games LF. The current metrics are higher on Bay's defensive prime a few years ago.
RF thinks he was ManRam type awful in '07 and '08 and poor defensively throughout his career. It also WASN'T due the home park as Bay actually grades out as a significantly better fielder at home in both 2007 and 2008 (although most of it was Pittsburg). Without the extra 60 or so flyball opportunities in '09 he would have graded poorly in '09 as well.