Depends on how you use him. He wasn't useless when he was taking Porto apart. Remember this?
Wenger was devastated when Nasri betrayed him and left. You should read that interview he did with l'equipe. He was still learning and developing, and Wenger would have made him one of the best in the world.
Not gonna dispute that he's a bottler though. No one can. Still, that can be trained out of a player. Remember how much of a bottler C-Ronaldo was when he first joined United? Or how Adebayor couldn't hit a barndoor, then scored 30 a season? Players grow and players change, some take until their mid or late 20's -- like Drogba or Bergkamp.