I keep waffling on buying a Powermac G4 for $40 locally. I think it'll boot OS9. If I stay indecisive for a few more days I'm sure it'll disappear and make the decision for me.
I would only get it if you really need to use older software that is not available on a current system. Otherwise, it will just take up space (also, which model... Sawtooth, Mirror drive doors?)