Brett Gardner was drafted by the Yankees in the third round in 2005, from the College of Charleston. Speed was his calling card, speed and the ability to draw walks, but his power was questionable. He hit .284/.377/.376 with 19 steals for Staten Island in the New York-Penn League after signing. I gave him a Grade C+ in the 2006 book, noting that I thought he was a slight overdraft, but that I thought he could be a useful player if he showed enough pop to survive at higher levels.
Gardner hit .323/.433/.418 with 30 steals in 63 games for Class A Tampa in 2006, then .272/.352/.318 with 28 steals in 55 games for Double-A Trenton. I kept him as a Grade C+ in the 2007 book, noting his speed, willingness to take walks, and defensive ability, but remaining doubtful that he would show enough pop to start. I wrote that he had "an outside chance to become Juan Pierre, but I think Jason Tyner-with-more-walks is more likely."
Returning to Trenton to begin 2007, Gardner hit .300/.392/.419 in 54 games with 18 steals, then hit .260/.343/.331 in 45 games for Triple-A Scranton with 21 steals. My analysis didn't change: I kept him at Grade C+ in the 2008 book, again noting his ability to get on base and swipe bags, but again noting the lack of power and projecting him as a fourth outfielder.
Gardner hit .296/.414/.422 this year for Scranton, with 37 steals in 94 games. In his major league action, he's hit .202/.263/.279 in 104 at-bats. Obviously that kind of performance is unacceptable. He's stolen 11 bases in 12 attempts, which is excellent, but otherwise he's been quite weak offensively. His plate discipline, which was terrific in the minors, has not translated well to the majors, with just eight walks and 26 strikeouts in 104 at-bats. And the lack of power is obvious for all to see.
What does the future hold? Despite the early problems, I still think he's got a future as a fourth outfielder. Gardner's track record is to thrive at one level, then struggle a bit in his first shot at the next level before adjusting and doing better in the second try. The lack of power is always going to be an issue, but he should get at least some of the plate discipline back. Not all of it: he doesn't have enough pop to scare pitchers into giving him excessive walks, but I expect much of the patience will return in time. His MLEs show him as a .250-.280 hitter with a .340-.370 OBP. The bottom range of that is unacceptable for a regular, but the upper range would be OK given his speed and glovework.
I think the original assessment of Gardner as Jason Tyner with more walks is still a good one. Whether that's enough to be a regular depends on the style of team I suppose. Gardner's glovework in center field is well-regarded; his arm is weak but he has excellent range. If you're getting enough power at other positions, Gardner in center field is plausable, but personally I still think he's best off as a fourth outfielder. HIs offense will be marginal for a regular, although if he hits at the top end you can make a case.