Okay, so a strange thing is happening with my cursor!
It occasionally disappears completely and won't come back without a hard reboot. It's a standard Mac mouse plugged straight into the keyboard and the keyboard plugged via a USB extender into the G5. I originally thought it could be signal degradation via the USB extender, but the keyboard is still active and mouse sensor lit. So I'm erring toward this being a software issue.
Anyone got any ideas?