I have the 2.5ghz Dual G5 Air Cooled PCI-X and its a good machine aside from these two problems:

OS X 10.4 causes power supply to chirp

Power Supplies die, must be replaced with a repaired one to avoid the problem

A pain to take apart

Its a pretty fast Mac if you stick with period PPC software. They look cool too, but all that size is for cooling, not really looks. The motherboard could had been condensed if the G5 did not run so hot.