So far, he hasn't shown much besides speed. His speed is terrific, so I think a lot of us (including myself) see that speed and think it is a great weapon and there has to be some way we can capitalize on it. The problem is, he hasn't shown much ability to do anything besides be very fast, I haven't seen any great blocking or catching out of him, and he doesn't look like he is ready to break a lot of tackles or make great decisions on his cuts. This leaves us in the spot where his main value is putting him in almost as a decoy, because when he is in the game, the defense has to respect the outside because he can take it to the house if he can get there, and the occasional outside run to open things up. If he can get better at identifying running lanes, and maybe get strong enough to break some tackles, he could be huge for us in the future because no one is ever going to catch him from behind.
I wouldn't write off any running backs on this team because they aren't getting a lot of carries or production, because plenty of good backs would be sitting behind a guy like Cobb. Should be opportunities for someone to step up next year.