Everyone knocks Vista, but I used it for years since it came out and never had any issues with it. I only recently upgraded to Win7 after upgrading my machine. Yes, it's faster, but I also upgraded everything else on the machine.
Tried Win8 during one of the previews and yea, it blows. It had potential, but they're trying to do this one-size fits all approach and slap a tablet UI onto it, that doesn't work on desktops. Not to mention they've made it almost impossible to use, completely unintuitive.