It makes me nervous when I see so many rankings from so many people who either haven't seen him throw or saw an inning or two and are ranking him ahead of every non-Pineda pitcher we have, and all but two hitters.
Taijuan pitched in 4 games, for 7 entire innings for the Mariners' affiliate in AZ.  He's a big guy with a good fastball, and he's raw as all getout, having only pitched 4 high-school games before his senior year.  He's a good athlete, since he's a basketball player too who could have played D-1 basketball somewhere...
But other than a few pitches on video, you know who saw the most of him?  Scouts for the ML teams in the 2010 draft.  And most of them passed on him without question, which is how he got down to us with the 43rd pick.
Maybe it's a Nick Franklin situation where the talent is much higher than was thought at the time.  I just find it interesting since he's a position switch (Walker was playing a lot of SS if I recall correctly) with a body of work as close to nil as you can get and still be a (supplemental) first round pick that he's ranked this highly by everyone, especially those that called him a cheap signability pick by the Mariners last year.  Note that I'm not referring to the guys at proballnw there.  Jon was complimentary of him even on draft day.
I guess it's not a lot different than Aumont, who barely pitched in the Frozen North before claiming a first-round slot from us and a high ranking in the system, but he was well thought of at the time.  This is more like Franklin somehow becoming the #2 hitting prospect in our system in February of 2010 after being "the worst first round pick / marginal backup prospect" in June of 2009.
It's interesting to me that former position-switches with raw but exciting pitching skills like Rafael Soriano and Mauricio Robles were poo-pooed for years even as they blew away pro hitters with lightning-like fastballs, while Walker will be 2011's best pitching prospect for the Ms once Pineda graduates - even though he has just a handful of innings to his credit and no pedigree to speak of.
I just wonder how much copying off of someone else's paper was done to get Walker that high everywhere. 6 months ago he was only the 70th best prospect for BA just out of the draft-eligible players.  Now, with 7 innings pitched and a few months passed, he's our #4 prospect.
Imagine how highly he'll be ranked if he gets sent to Everett and doesn't start pitching in earnest for half the baseball season.
Guess I'm just skeptical.  It's not his fault we have very few starting pitching prospects who can boast his upside.  If I was trading for Colby Rasmus, though, and as part of the package the Cards demanded one of Walker, Robles or Wilhelmsen, Taijuan would be headed for St. Louis, so I guess he's not #4 for me.
But I'd certainly love for the group opinion to be the right one, and I have no hard data and just a couple of frames of video to even suggest otherwise.  Go Taijuan - make us proud.
And may Wilhemsen, Robles, Beavan, Lueke, Pineda, Ramirez, Vasquez and all the rest do the same.
~G

I think it demonstrates that the M's only have 3 prospects with a good chance of being average MLB position players or starters.  I also think it demonstrates that many have decided that Walker has the highest probability of being a top of the rotation starter in the bigs of all the M's pitching prospects short of Michael Pineda. 
Sure it underplays the fact that he has a higher chance of never seeing AAA than he does of pitching in the all-star game, but prospect watching is, in large part, wish-casting. 

In an expansion draft, Ultra league, you'd have to protect Robles over Walker just on the attrition factor alone.
Even assuming that Walker had ever come to spring training and massacred a bunch of ML veterans, as Robles has done, he'd still be 18 and would have four years of injuries to avoid, to get to where Robles is now.  But in reality, if Taijuan Walker came to ST next year he'd be pummelled like a popup punching clown.
No way in the world Taijuan Walker ranks #4 in the M's system.  That's not a defensible position.

It's un-cool to be optimistic about Seattle Mariners (TM) prospects.  Two years from now I'm sure Walker will be ranked 8 spots behind whichever #1 pick doesn't yet have Mariner icky on him.
....................
Practically all ML orgs have more than 3 prospects, I would say.  The amateur draft alone produces 30-40 WAR per year.  The bias against Mariners minor leaguers at times reaches silly proportions.
What do any of the 'net rats go on, when dismissing (say) Carlos Triunfel, other than that they think at age 19 (+1 DL year) he should be a star in the high minors?  What is their basis for evaluation?