The G5 quad with it's liquid cooling system is even heavier, I know this cause I have both a g5 dual 1.8ghz and the g5 quad 2.5ghz.I'm posting this message from the G5. Everything seems to be working just fine; the G5, the cinema display and its' power brick.
I must say though, this is probably the heaviest computer I've ever lifted! What did Apple do, put lead in the bottom of this thing? I had to schlep it up the ladder-well to the third deck of my apartment building where I live. It was about as bad as when I moved in and moved all the furniture!
Anyway, I'm going to break out the Leopard disc and do a clean install on it now.
But they are 'sweet' machines...