Just to chime in with my horror stories on Vista.
New rig came in a few weeks ago, out of the box the sound didn't work. Apparently that hits a lot of people with soundblasters, so I had to waste a good 5 hours tweaking registry settings and rolling back BIOS flashes and so forth before I got it to work. The culprit, a little service program in Vista that conflicts.
Hilarity ensues last night when my activated version of Vista decides that its all of a sudden not activated. Reentering the product key I was given, doesn't work 3 times, then all of a sudden it does. Except now theres a little message in the bottom of my screen that says its not activated (even though it says activated in the control panel and in the software M$ uses to diagnose this).
So I roll back to an old restore, clean boot, etc. Problem goes away, everythings fine and dandy. Ooops, next restart, it prompts me to reactivate again. This time, the product key fails completely and im locked out of doing most things other than surfing.
Several angry phone calls later, more registry tweaking and rebooting, +a new key and I think maybe finally we've figured it out (and I have no idea what the problem was to begin with).
Either way, a pleasant way to spend a morning, when I should be getting real work done.