Apparently US data centers consumed 61 billion kWh in 2006 (according to this EPA report (PDF)). That sounds like a big number, but I like to judge these things by my favourite Big Energy metric: how much mass would you have to completely annihilate to get that much energy?
Well, assuming I crunched the numbers correctly (ie, assuming I can blindly trust Google's calculator), that amount of energy can be expressed as 2.196*(10^17) joules, which, when divided by the speed of light squared yields: 2.44 kilograms.
Given that the same EPA report claims that this energy usage statistic accounts for 1.5 percent of the total US electricity consumption, that means that to power all of the US for a year, you would need to annihilate 2.44 divided by 0.015 = 163 kg of matter.
That strikes me as a remarkably high number. It means that if I were to encounter my antimatter twin (and both of us weighed somewhere around 68 kg), even if we did fully annihilate each other and even if all the energy from this event were captured (and stored perfectly until needed), this would only power the US for somewhere around 300 days.
This saddens me, because it means that my human-antihuman power supply will require a disturbingly large number of sacrifices to keep running.