I just plugged my UPS into my Kill A Watt to join in the fun.

Computers off, Drobo in standby, two 19" LCDs in standby = ~42 Watts

Dell 530S with Core 2 Duo 2200 (2.2GHz) at idle, but Drobo accessing = 200 Watts
Both cores pegged at 100% and Drobo accessing = 237 Watts
Both cores pegged and PowerMac G4 1.0GHz turned on at idle = 304 Watts

Turning the monitors off results in a power consumption drop of 30 Watts each.

Is is possible the G4 with two hard drives powered up only consumes 67 Watts, or is it more likely the Kill A Watt isn't very accurate?

I'm actually pleased with these results since the Dell box and drobo stay on 24/7. 200 Watts is less than I expected.