Since my Ubuntu/Windows dual-boot went so well, I decided to try it on my Powerbook G4 too. And Ubuntu is great - although there was a slight snafu getting my wireless card to work. Just
followed all the instructions on this page, installed Network Manager, and removed all lines except for lo and eth0 in my /etc/networking/interfaces.
Mac-On-Linux was more disappointing. It installed just fine, and ran just fine, but I could not get more than an 8-bit color depth running OS X from MOL. Apparently this, and my sleep problems, have something to do with my nVidia drivers and is
not fixable. :(