Well, this stinks. Jarek Cunningham, who had easily the most impressive pro debut of any member of the 2008 draft class last year, has torn his ACL and will miss the entire season.
The good news, such as it is, is that tearing one's ACL isn't like a pitcher blowing his elbow out or something. That is, it doesn't seem to have drastic long-term effects and probably won't change the way he needs to approach the game. He'll be back at full strength within six months or so. It just means he'll miss the season, which certainly will affect his development, but it could be worse.