What speed are your G4s? I have a 1.33G G4 in my PB and I don't see much CPU usage.
The one thing I know that does hog CPU is using "secure delete". If you have that enabled, it's possible that Hazel is shredding a file. You may want to consider not using that feature in that case.
Otherwise, next time you notice high CPU usage, could you do the following?
- Start up Activity Monitor (located in /Applications/Utilities)
- Select the hazel process gone amuck.
- Do "View->Sample Process" from the menu.
Send me what you get from that and I can try and interpret what's going on.
Thanks.