A g5 has been my daily driver for a couple years now, sinse I lost my A3000 hard drives. I have no experience yet with MorphOS, but, I think I will give it a try when it will run on G5 hardware.
I will keep OS10.4 around on the G4s. OSX is descent but always seems to be forcing me to do it Apple's way. MorphOS might be a nice change in this regard.
So, what's the ETA?