PowerMac G5 Quad 2.5:
Primary work machine. Anything to do with regular work, plus encoding, compression, drive formatting and troubleshooting, Remote Desktop administration, network administration, diagnostics, a little gaming, and occasionally running XP for that odd thing that needs XP instead of Win7 on my MacBook Pro. Runs Leopard most of the time, but I have it set up to dual-boot to Tiger off the Constellation when needed.
PowerBook G4 Titanium 1 GHz:
Writing (that keyboard is the BEST), e-mail, web browsing, running OS9 native games and applications (the last, fastest PowerBook to still be able to boot into OS9), alternates with my MacBook Pro for watching DVDs before bed.
MacBook Pro 2.6 GHz 15" (Early 2008):
Oh wait, no Intels in here!
PowerBook G3 Wallstreet 292 MHz
PowerMac G4 Digital Audio 733 (upgraded to Dual 1.8 GHz 7448s + GeForce 4 Ti4600 128MB)
Mac mini 1.5 GHz
SuperMac S900/250:
Not much these days other than making up my one-man Apple museum.