I'll stick with XP for now.
I don't have any need to upgrade to Vista, and the cheap versions are crippleware anyway. If my stupid laptop's sound card actually worked with Linux (it worked with one distro straight out the box, but it was a pretty cack distro TBH), then I'd switch to Linux full time I reckon.
I just don't see what you people do it for. Windows is the same as the previous version at twice the price, except for Vista which is loaded with stolen ideas from UNIX and some from MacOS (Bill Gates has 30% shares in Apple). XP was just 2000 with noob-proof features and a different interface, there was very very little in the way of underlying differences.
Leopard is just Tiger with a few features you'll never use (Time Machine basically needs a server to back stuff up onto, who at home has a mainframe? It just isn't practical). Spaces, what's the point? Hell, if they'd just fix the bug when the Dock packs up and stops animating at random, rather than putting in stupid flashy features that are ultimately useless.
I won't be buying Vista... I'll just ask Renegadeandy to "acquire" me a copy