I have all three. The dual processor 2.3 is an excellent machine. The Cube has been upgraded to a dual G4@ 500mhz, but is still much, much slower on the web. Mine sits on a shelf mostly, whereas the G5 is used constantly.

Failed Cube power supplies typically fail because of a single capacitor. I started a thread back a couple of years ago and wrote of how best to get it open and fix. Not a huge job but a fiddly one.