Man Utd don't need Van Persie. IMO all it is is an attempt to get one over on Man City who were linked with him for a while. Ferguson's usually pretty wise with his big value transfers but it does strike me a bit as "shit, Man City have overtaken us, quick, buy RVP!"
Don't get me wrong, he's class and him and Rooney will be devastating in a fair few games. But he's not really what Man Utd need.