Sarge has struggled mightily this season. He's currently sitting at a -16, third worst on the team. It's difficult to give him too bad of a grade, because he still has averaged over a point every two games. Of course, this is far below what was expected of him entering the season, fairly or unfairly.
He has been playing better of late, and shows promise for the rest of the season, not to mention the rest of his contract. I've read articles that say that the expectations placed on him were unfair, and that he's not really the puck-toting defensemen that everyone in Pittsburgh seemed to expect. I think he's starting to adjust.
The biggest disappointment for him, aside from his seemingly aloof play on the ice sometimes (something somewhat common here in Pittsburgh in the past), has to be the number of penalties he's taken. I think that it's only a matter of time before he adjusts. Of course that time could be next season.
Overall, I'm not going to call him a bust... not with how the rest of the Pens season has been going. If he continues the same performance once the teams starts to perform better, then I'd be willing to reassess.