Personally, I'm running a dual boot - Vista and XP. Vista has a very nice look to it. But unless you have one of the higher flavours such as business or Ultimate, it's really just more of a resourse hog. I have ultimate. I don't use any of the features that come with it. I'm sure if you wanted all the extra and security such as encyption, thats great! I don't need any of it so I just stick with XP. First - It works, its been out for a while so they have alot of the bugs fixed in XP, unlike Vista where it has just been released and obviously still has major flaws. EG: the LACK OF DRIVERS FOR CERTAIN DEVICES grrr.
I'd say, if your an average user, it's really up to you. Vista's nice, but don't go out of your way to get it. XP will sufice.