Barkley has had some bad games this year, for sure. If he had come out last year, he'd have definitely been the 3rd QB in the Top Ten, if not the Top Five.
Word on the street here is that Lane Kiffin is a goner. Pat Haden and USC believe that Barkley has regressed and not improved this year and to them, the blame lies with Lane Kiffin. Their defense is absolutely loaded with talent but they're playing an antiquated scheme.
The bottom line is that Barkley is a mature young man with four years as a starting QB at a Top 25 school. He has all of the immeasurables you'd want in a QB including strong leadership and great character (in addition to respect of his teammates) and he's not lacking in any measurables. Sure, more arm strength would be nice but he's certainly not lacking in arm strength.
He'll need to go to a team willing to tailer a WCO offense around his skills and if so, should be a very good NFL QB. Unlike Sanchez and Leinart, Barkley LOVES football.
That said, I think it's silly to make any determination now. Wait until after bowl season, after the Combines and after a new GM and coaching staff is in place.