No real bugs, I've been overall happy with it once I got used to where stuff was.  Sometimes it was annoying, like finding where the "run" start menu item.

UAC is a pain in the butt (turned mine off in less than 3 days), some older apps don't like vista, or so vista says, but might run anyway despite what vista warns about,  ancient hardware won't have drivers, and make sure you have plenty of memory, 2gb seems to serve me well.  Otherwise, it's been stable, and pretty quick.  And I push it quite often doing development work.