My latest project has been to load and run Debian GNU/Linux on a Power Macintosh G4/466.
The box came to me with no disk drives and 128 MB of RAM. I upped the RAM to 384 MB, and I installed two hard drives.
Besides the stable Etch distribution of Debian, I experimented with the Fedora
Linux distro as well as OpenBSD.
Fedora installed, but configuring X for the GUI video didn't go very well. I probably could've gotten it to work better with information from the xorg.conf file that Debian built for me automatically, but since the system was extremely slow under Fedora, that only made the choice of Debian Etch (which seems made for and tuned to the G4) that much easier.
I really wanted to see how the G4 would do with OpenBSD, but while I was able to install it on two occasions, on neither of those was I able to get the system to boot. The regular FAQ for OpenBSD has excellent instructions on how to install it on an i386 machine, but the supplementary material for doing the install on MacPPC was less than helpful (or not helpful enough to get the system to boot).
So I went with Debian. I installed the system on one hard drive and am using the other to back up the /home directory via rsync.