I have a Shuttle cube (running OpenBSD for work) and would *love* to replace it with a G4 cube; they're so cute!

Are you planning on upgrading it? You could probably do dual 1.4s, at least. With a GeForce 6200, you could push a pretty big panel with it and it would rock MacOS X.

Then again, it's probably a really sweet MacOS 9 machine even in stock trim.