I'm not sure why anyone would consider upgrading to Vista.
Also, like mattmaroon above, I fail to see why people hate Vista so much. I have no problems with it. Its stable, has support for my hardware and seems fast enough. And I run the x64 version, which is likely more quirky that the 32 bit one. I did do a fresh install, so I maybe upgrades are more problematic. I have also been a Mac/Linux user since the Windows95 days, so have little experience with XP and 2003.
That, for me, became so annoying after a few days I turned it off. (I do keep running into inexplicable instances where I am not allowed to delete or move files I created without engaging in much unintuitive file property manipulations, so the machine still seems to be boss of things.)
Vista is amazingly annoying in so many little ways. I suspect that is true of all OS, and people just become numb to them, but Vista seems keen on reminding me what "opinionated software" is all about.
So far the only thing that keeps me from replacing Vista with XP is the pre-installed Media Center software.
(I already set up the dual boot for Kubuntu, for Serious Computer Usage. :))