Vista was the worst OS that MS has released so far. Look at the video reviews from Bill Gates, he almost denies Vista's existence.
Everybody was disapointed. As ahslan has said, Windows 7 is a Vista that works somewhat correctly. Surprisingly, XP still has more support overall if I am not mistaken. Vista just has more memory support which means nothing since the OS itself has performance issues. Sure, Windows 7 is an improvement but nobody trusts MS no more since Vista came out. As far as software support is concerned, nobody cares at this point.
Otherwise, XP wouldn't be selling at a good retail value.
To answer the initial question, performance is better, the interface is cleaned up, as far as support goes, that is not clear.
XP SP2 is going to be around for quite a while, get use to it.