It's indubitably too high of expectations, but I've felt most of the year that Grady has underperformed. After all, his age 24 season (92 extra base hits!!!) was so good, it seemed like he was going to make the leap at 25 into super-super stardom.
He's responded with a .280/.384/.468/.852 line, opposed to last year's .290/.367/.533/.900 rates. Right off the top, we can see that his power has dropped, which accounts for the drop in OPS.
This is still great offense for a centerfielder. And, from the looks of it, there's absolutely zero reason to not expect a huge season next year.
One of the most encouraging signs is the spike in his walk rate. In 2005, his BB rate stood at 7.4%. In 2006, it upped to 10.4%, and in 2007 it is at 13.2%. This continued growth is one of the most exciting things he's shown.
From a luck/unluck perspective, it appears that he's been right on target. While his BABIP looks high (.340), it is right in line with his 05/06 numbers (.335 and .342 respectively). His line drive rate has ticked up from 19% last year to 21% in 2007. (I don't have the numbers from prior years.)
Two things allow Grady to consistently keep such a high BABIP: his speed and his GB:FB ratio. His groundball percentage is a low 35% (34% in 06), and his 21% line drive percentage leave him with a strong FB percentage of 44% - and fly balls are more likely to turn into hits (also why extreme ground ball pitchers like Fausto and Westbrook are so successful).
Historically, Grady has punished RHP and been dreadful against LHP. No more. This year, his splits are pretty even, with a .276/.393/.479/.872 vs. RHP, and a .288/.369/.451/.820 against LHP (170 PA). In comparison, in 2006 he posted lines of .329/.416/.586/1.002 vs RHP and .214/.290/.427/.717 against LHP (239 PA). So, when he returns to his usual RHP bashing days, we're going to see something closer to a .950 OPS than the .850 we're seeing now.
He hit 53 doubles last year, an indicator of future HR power. So, if you're in fantasy leagues, trade for him, because next year he's going to explode.