I've got 3 G3s... none of which I use. An AIO, a B&W and a PB. I haven't tried to load OSX on them but knowing how bad it is on my G4 (see sig...), I wouldn't bother.
I've got plans for the AIO, possibly involving the B&W logic board (but possibly not... I may use a G4 board I have sitting around, if it works, or pick up a MDD G4 board instead...) but I don't really feel like spending the money to implement them right now.
The G3 was a good chip though; iirc for applications that don't use AltiVec it was actually faster, clock-for-clock, than the G4.