Workstation: Vista Ultimate 64bit since it was first released. Apparently I'm an anomaly, but the OS has crashed only once in that time. I'm usually running VMWare (FreeBSD) with multiple xterms/nedit windows for development, as well as the usual browsers, office apps, Quicken...
Laptops: Mac OS-X 10.4.x, 10.5.x - Thank god apple moved to x86 arch..
Servers: FreeBSD 6.x (stopped using Linux ~10 years ago...)
All of the machines are online 24/7. (Yeah I know, I'll go plant a tree...)
I've found that buying solid hardware makes a world of difference in OS reliability & uptime