Oh, one other thing. Reverting to XP will not be possible for people who need new hardware. Microsoft has already stopped, or will very soon stop, providing new XP licenses to the big computer manufacturers. So if you buy a new machine, chances are XP won't be available at all, no matter what kind of tantrum you throw.
You might think you could just try putting an old copy of it on your new hardware, but there are already quite a few units out for which XP drivers were never and will never be written. My brother just picked up an HP laptop that's been available for about 9 months now that suffers from that. He can find no XP drivers for the ethernet card. He thought he needed XP for some music authoring software, but it turned out the vendor updated it for Vista about two months ago.
The only applications I own that won't work in Vista (even in XP compatability mode) are some games. Not really a showstopper for photography...