Unfortunately, my experience has been that PPC linux has been a waste of time. It's really a bastard child, with most efforts being directed at X86 development and, recently, more to OSX than to PPC Linux. Many applications are kind of broken, support is minimal (I've tried four flavors!) and nothing that I really wanted to use worked. These were mostly music programs, cecilia, Csound, vspace, pvc, etc., but I don't imagine anything else is much different. Plus, with the new Mactels, I don't imagine support is going to get better...
Invest your time learning the ins and outs of your Darwin underpinnings, and be greatful that your mac "just works". (Out of the above, now, only Vspace has not been compiled for osx!)
Problems I've had have been
-audio never settled or worked well - alsa was wierd and everything else was broken
-trackpad on the powerbook I tried it on never worked... always had to use a mouse.
-as listed above, many programs that worked on X86 hardware with Linux did not on my PPC machine with PPC Linux
... the list goes on, but why bother?
If you REALLY want the Linux experience (Which I'm almost sure you don't if you knew how many hours it would take you just to get the machine up and running) put together a computer yourself. You could get a great machine going for under $1000 and run it legit...
-S