When I still used OS X, I ran a i386 Linux distro on my PPC iBook. Gnome worked, but it was too slow to be usable. It seemed pretty cool though.
I also used have the same kind of a setup for running Linux on from a USB stick inside of Windows. I never ended up using it though - since you have to wait for it to boot slowly in a virtualized environment, I found it easier to just reboot the actual computer in to a persistent live session off of the USB stick. Or more commonly, use SSH from a portable version of PuTTY, since I all I usually want is CLI access to my home computer. Peter: VBox requires installing software - so, if you don't own the Windows box, it may not be appropriate. And it takes time.
