I just replaced my home server with a low-power MoDT (mobile-on-desktop) machine, and I have been using one of these cool Kill-A-Watt meters to measure how much energy my new server and other devices use around my home. Get a Kill-A-Watt and start measuring. I recommend the P4460, since it adds a cool feature where you enter your energy cost from your electric bill and it calculates day/week/month/year costs for the device currently being measured. The power strip liberator is nice for avoiding covering up other outlets while using the Kill-a-watt.