I have XP Pro and I refuse to upgrade to Vista at this point. I plan on building another computer when I get the money. My step-dad's PC has Vista and I've hated using it. The only difference I see in Vista is that there's a sleek new Interface that looks cool and organized. In reality all it does is hide all the useful commands... like "SHUT DOWN." On top of that, I had compatibility issues with Vista and couldn't get some software to work on it (some photo-editing software that came with my step-dad's scanner).
Microsoft finally got everything right with Windows XP... unfortunately, they screwed themselves over by doing so. There's little reason to upgrade to Vista, and those few reasons are usually outweighed by problems caused by Vista. The only option Microsoft had was to force Vista on all new pre-configured PCs. I feel sorry for the people who don't know enough about computers to build their own. A lot of them complain about Vista, but can't really do anything about it.