On the right he is completely and utterly lost. On the left he's been quite good, I like him better there. His best position though is Iniesta's position, I have no idea why Wenger doesn't let Nasri and Cesc play the Iniesta and Xavi roles.
Anyways, Nasri is not going to Man Utd. Absolutely no chance. IF he does, Wenger might as well resign as he would have completely disgraced himself. One week after saying that certainly we would not sell him to United, we do? That would seriously undermine his position. United will throw good money at us, but we don't need it.
He will sign an extension, and if he doesn't he'll be flogged abroad.