I just installed the OSX 10.4.9 update on our PowerMac G4/533 at home and had a little bit of weirdness. The first time the machine was rebooted after the install it took several minutes for it to actually start booting, leaving the screen white until it was ready - needless to say this was rather concerning, but I left it alone for a while and it finally kicked in a-ok. The Mac Pro at work had no problems, however.