Multi processor desktop: Windows 2000 (seems to be better than XP for SMP performance, based on trying them both)
Laptop: Windows 2000
Web browsing box: Windows 2000 (used by parents, so needs to be more robust than win9x series)
Multi processor fileserver: Linux (needs reliability and stability... runs 24x7)
Cabinet pc: BeOS (for kicks)
Car pc: Windows ME (for bootup speed)
Xbox: Linux (was my old Car pc)
Web proxy/Firewall pc: Linux (squid + iptables firewall)
SGI: Irix
A7000: RiscOS 3.6 / NetBSD 1.4
A3010: RiscOS 3.1
Amiga 1200: Workbench 3.1 (wanting an accelerator!)
Amiga 500: Broken :-(
+ assorted old 486's and a p166 that I need to rebuild sometime.... (probably as dedicated DOS game machines).