Windows 7 (Beta testing it at the moment) is very nice actually. I'm running the 64 bit version and it's stable.
Otherwise I run Vista Ultimate for the main OS since my puter died.
I didn't reinstall Carrara yet... and it has me worried now, seeing that it doesn't play nice with the 64 bit version.
(Though I have a feeling I'm going to ditch Carrara for Vue some time, so not sure if I'm even reinstalling it...)

Silke