Ever since installing 9.04 I've had intermittent problems with USB peripherals--all two of them. The important one is the printer, an Epson 740, which sometimes would print just dandy and then sometimes would crash everytime a document got spooled.
So I took the Power PC Enbler 9.04 out of the System Folder, and ever since, I've had not a single problem with the printer. In fact, the computer feels more stable with plain vanilla 9--haven't had a single crash since I took out the "upgrade." I should say that I'm talking about a G4 400 MHz with 256 MB of RAM as well as a Rev A iMac with 160 MB RAM.