Google just announced that its data centres use 260 million watts to power Google searches, YouTube videos, Gmails, ads and so on and so on. That's about a quarter of the output of a freaking nuclear power plant. Or more power than Salt Lake City uses.
Basically, it's a ridiculous amount of energy, enough to power a city of 100,000 to 200,000 people. For comparison, Salt Lake City, Utah 'only' has 186,440 people. Google reasons that it's okayish to be using that much power because people are actually saving energy by using Google (searching instead of using the library, let's say). The average Google user's energy usage is similar to running a 60-watt lightbulb for 3 hours. Not bad for all the cat videos we watch. [NY Times]