Using it to monitor my new QX6700 system (spec in sig) this is what I found:

Idle: 200 watts

1 core under load: 250 watts

2 cores under load: 280 watts

3 cores under load: 295 watts

4 cores under load: 310 watts

4 cores + 8800GTX loaded: 390 watts

I applied load by running instances of SP2004 on each core, and 3DMark06 to load the video card. Given that the QX6700 has TDP of 130 watts, it would seem that when idling it's probably consuming roughly 20 watts. Putting all four cores under load adds 110 watts. Loading the 8800GTX adds another 80 watts. Overall I was pleasently surprised to see that under max load I was only drawing 390 watts. I purchased a 750watt PS under the assumtion that full load would be 490 watts (roughly 65% utilization). This means I've got even more headroom than I was planning on. I suppose this goes to show that those new 800watt and 1000watt Power Supplies that are coming out really are overkill.