Well, I have a B&W G3 running:

8.5, 8.6, 9.0, 9.1, 9.2, 10.0, 10.1, 10.2, 10.3, and 10.4.

From five partitions. (One 'Classic' and one OS X on each partition.)

My G4 Digital Audio runs 9.2 and 10.0 on one drive, and 10.5 on a second.

My netbook dual-boots Linux and XP.

My 'nettop' dual boots Linux and Win7.

My server dual boots Linux and Windows Server 2008 R2.

My primary "PC" desktop dual boots Windows Vista Ultimate and Windows 7.