If you mean guys that could under perform for where they are a drafted, I found question marks for everybody on the list except one.Steven Jackson- I couldn't think of a reason other than injury that he would under-perform, but I'm sure somebody will post something I didn't think about for him too.
Regression to the mean. Steven Jackson last season had the fifth most yards from scrimmage in NFL HISTORY. Given the fact that, outside of last year, he has never finished in the top 10 in any major statistical category, combined with the fact that his season last year was almost as historic as Tomlinson's (even if it didn't get as much press), I don't think it's that hard at all to envisioning Steven Jackson remaining fully healthy and still drastically underperforming expectations.This isn't to say that I don't like SJax. I'd take him #2 overall, too. I'm just giving you a reason why he's a bust risk.