Flame Bait
I have been trialing Vista for a Multinational with all of their enterprise applications and I have to say about 90% of them worked no issue. The system its self is far more stable than XP (the Dell GX620 that I am running it on came with XP and was less stable before I put vista on also not exctly massive hardware spec on a GX620) in fact the OS has not crashed in the year and a half I have been running it only applications have. The increased security that UAC and the sandboxed IE would be a good enough reason for a company to consider not downgrading to XP the only bit of FUD that I would agree with is that it is not worth either the software or hardware costs to upgrade old equipment but any new kit that comes with vista will keep it also as we move to server 2008 the other security features such as Network Access Protection and the enhanced RIS Windows Image Manager will make vista even more attractive.
I also use vista at home and that is on a three and a bit year old Acer 5020 running vista x86 at the moment but I plan to try x64 on it. The only thing I did to the three year old laptop was upgrade it to 2gb of ram but this was done before vista was released and while it is a little slower than XP it is not so much that it is noticeable when using for everyday things like playing guildwars or hellgate london (hellgate BTW recons that I need a 2.7ghz proc to play under vista but it runs quite smoothly with the 1.6ghz amd in the laptop)
Take another look at the security features of vista and also at UAC it is not something that should be turned off, if it annoys you and you have one of the none home versions of vista just set it to automatically elivate the requests that way at least you can still benefit from the sandboxed IE.