I've tried to stay out of this one because I''ve repeatedly made my thoughts on Jenas clear, but it's a big discussion now so I thought I'd come repeat myself again!
Many times I've watched matches and haven't been able to say exactly what input Jenas has, but I do know that we play better as a team when he's on the pitch. He started getting a lot of grief this season while he was injured, which I thought was unfair, but have you not noticed that our turn up in form has coincided with his return to a regular starting berth? That's happened time and time again - it's not just luck that does that, it's his contribution.
It may be that he instils confidence, it may be that he knows returning players like Keane, Chimbonda & Defoe well (we've hardly had on-pitch continuity over the last couple of years so that's got to help), but I think Swissquaker's right. Sometimes he seems to have quiet games too often but when you really watch out for him you see that his off-ball work is great: check out the post-highlights analysis on MotD, whatever the move is we're involved with you'll see he's positioned expertly. Whether it's causing him to be double-marked so he doesn't get a ball but someone else has a chance to run and pick it up, or he's widening the midfield so Modric's got more room to do his magic, or he's dragging a defender out of synch so the offside trap fails... whatever, he does a lot of it. He may not be world class (I hate that phrase!) but he's far better than he gets credit for.