I've been using OnyX for some time, each time updating it to roughly match my OS. I started at 10.4 and am now up to 10.4.6. Never a problem, always reliable. I'm now runnig OnyX 1.6.9 on my G4 PowerBook and iBook about once or twice a week. There seems to posts below of some with issues. Perhaps running Disk Utility to fix permissions might be a good idea before first use with OnyX, and if you suspect you may hose your hard drive, back the who thing up first to a Firewire drive to be safe. (A bootable external partition for recovery is not a bad thing to do anyhow) Regardless, I highly recommend this utility and would be lost without it!