At least, that's what most of us assumed. Mac OSX Hints jumps on Yet Another Opportunity To Prove Me Wrong, this time posting a step-by-step guide to booting your PowerPC Mac with a USB 2.0 device. The procedure has been tested on the newer iMac G5 models (with the ambient light sensor onward) and the 1.33GHz 12" PowerBook G4, but it's worth giving it a try on other newer PPC Macs, too. It's pretty tricky, involving some fancy Open Firmware manuevering, but the procedure looks promising.
Give it a try and let us know how it works, ok?