Terra Soft Reveals Linux/PPC Hardware Solution
I ran OS 9 (Classic) under Mac-on-Linux for some time. Anything that didn't require direct hardware access worked pretty much flawlessly; MOL emulates the essential hardware (video, hard drive, input devices, NIC) pretty well. But you wouldn't be able to for example use OpenGL apps. Photoshop ran great but it would never talk to your USB scanner. In this regard it's just a little bit more limited than Classic mode under OS X, though. I never ran OS X under MOL but I assume the limitations are similar. The vast majority of things that run under OS 9 just worked.