Globe and Mail: As people turn off the lights for Earth Hour this evening and ponder their electricity use, one of the world’s most rapidly growing power guzzlers — for which nearly everyone carries responsibility — is largely hidden from view. It’s the network of data centres and their servers that are the invisible backbone of the Internet. The popularity of all the twittering, blogging, music downloading, and Facebooking has had a little-known environmental downside, by boosting the demand for …