I just got a new UPS for my computer set up that offers real time power consumption for my computer.
Playing WoW uses around 100W (i.e increases my power from total power from 422 to 528W) - this is just walking around not in raid or anything special.
At 22c per kWHr, that 100W costs me 2.2c/hr to play wow.
I play around 100 hours a month - so that's an extra $2.20 or more to play WoW per month just for the electricity.
Anyone else ever thought about how much electricity companies get from people playing high end video games