I've been using Vista Ultimate for around 3 months now (on 3 PC's) and can honestly say, I haven't dropped back to XP once.
As Jim has mentioned, you're looking at 2GB's worth of RAM to get the best from Vista and a dual core CPU (or fast 64 bitter) is really needed. Vista is a serious resource hog and if you have a modest spec PC, I really wouldn't bother upgrading, it'll be hell for you!
If you have a decent amount of machine grunt, it's a recommeded OS and the new 'toys' such as the Aeroglas feature, come in more than handy when juggling multiple windows. M$ haven't moved things around too much and everything you are used to such as services, utilities etc, can be easily found with a little bit of searching.
Is def. due a service pack tho.
