I installed Panther on my G4/400 MHz Powerbook. Runs faster and the only problem I have is that the "c" key has to be held down longer to type the letter. A pain. Didn't do this before the install. Tried just doing the update, but srewed the system up, had to wipe and do a fresh install.
Now I'm installing on my G4 desktop 1GHz, wiping the drive and installing fresh.