Currently running on an Athlon64 3000+ / Debian-stable machine. The only time it boots Windows (2000 pro) is to play games at LANs.
If I had my choice, though (and the funding), I'd be running on an SGI Onyx4. IRIX on MIPS processors is far preferrable to anything else, and runs Maya really fast. Unfortunately, the base system (2 700mhz MIPS processors, 2 ATI FireGL graphics pipelines) starts at around $40,000 and change.
Other machines in my house:
UltraSPARC IIe 250mhz x2 / Solaris 9 (Sun Ultra Enterprise 3000)
MIPS R4000 175mhz / IRIX 6.5.12 (SGI Indy)
Athlon XP2000+ / Debian-stable (NFS / netboot server / cluster manager)