Well for a dual core chip it's pretty energy efficient I think. Try putting in two 2900XTs and two 8800Ultras just to put it in perspective
If there's one thing I'm glad for it's that GPU companies finally start to take power usage seriously. Heck, this might mean that I have quite some life left in my 580W PSU, provided it doesn't smoke. Seeing the current trend, I wouldn't be surprised if an A-brand 500W PSU would be enough to power about any single card system.