I hear he doesn't walk too much (though that's improved recently), not too much power (16 career homers). His hallmark has been a very high average, .323 in the minors for his career and .341 at Pawtucket this year, though so far that hasn't translated to the major leagues. Supposedly has the "potential" to be a future batting champion. Good fielder, and he generally has about as many steals as homers.
So... I expect him to start next year for the Pirates (whose second basemen this season have been the murderer's row of Pokey Reese, Jeff Reboulet, and Abraham Nunez) and put up maybe .285/10/75/15 or so numbers. Eventually I'd project .320/20/90/20 maybe, though the 20 homers is a little unlikely. He's a classic overachiever, so they say, and he's drawn comparisons to David Eckstein.