One of the only reasons I saw to upgrading to Vista, WinFS, was canned.
http://en.wikipedia.org/wiki/WinFS
I've used Vista, it's basically bloated XP with a bunch of crap I don't need. What else is new with MS.
As usual, I'll wait until one or two significant revisions of the OS has been completed before I install it. XP works just great for me.