Computer Hungry, Need Power!

Last week we were having some storms here in San Francisco, so I plugged my XP machine into a monster back-up power unit, an APC Back-UPS XS 1500. It’s supposed to be good for 900 watts, which is good since my previous decade-old back-up unit was only good for 450 watts, and you know, computers have gotten a little more power hungry since then. The power flicked a couple of times during the storm, but I just kept on working.
But shortly after plugging it in I realized that the unit has a display with a power-use readout on it. How cool! So I thought I would measure how much power my computer is ACTUALLY using. These days, with high-end graphics cards and power-hungry CPUs, I always make sure I buy a 650W power supply or larger. I figured my computer was probably really chomping down on the power.
Fortunately that turned out not to be the case! My Core2Duo XP machine, with an ATI 3870, one DVD drive, and three SATA hard drives, boots up using about 184 watts. That is a long ways from what I had thought. Of course, that is at boot. Starting up Outlook, Firefox, etc, has a negligible impact on the power requirements, though. When I start up World of Warcraft and run around on the other hand, the power utilization goes up to 270 watts. Still, that is nowhere near what I had thought.
Now I want to plug in my LCD, and SLI Vista machine, and see what those say. Mmmm fun!
EDIT: Bret from Sony suggests that anyone interested in monitoring their power utilization get a Kill-a-Watt. I didn’t realize they were so cheap… 20 bucks on Amazon right now!