I ran into a rather interesting discovery regarding power consumption of my PC while in sleep mode.
Using a Kill-A-Watt I measured how much power my computer uses.
While under normal operation, I use around 120-170 Watts. This is reasonable for my hardware - Core 2 Duo 7200, GeForce 6800GT, 22 inch ViewSonic flat panel.
Then I tested the watt usage while the machine was in a "Sleep" state. The result was a surprisingly low 13 watts.
I noticed that I could not wake my computer up using my USB keyboard, only the power button. So in Control Panel -> System -> Hardware -> Device Manager -> Keyboards -> Power Management I checked "Allow this device to bring the computer out of standby". I then re-ran the test with the Kill-A-Watt.
With this option enabled my consumption during sleep mode went up to 66 watts! That's a 500% increase!
I leave my PC on 24x7x365. Looking at my last bill I pay .16 cents for a kilowatt. Having this option turned on will cost me an extra $75/ year. No thanks, I'll just push the power button to wake up from now on.
If anyone else has a way to measure energy consumption - post your results.