Amazing stats buried in a Wired magazine article:

"If it's necessary to waste memory and bandwidth to dominate the petascale era, gorging on energy is an inescapable cost of doing business. Ask.com operations VP Dayne Sampson estimates that the five leading search companies together have some 2 million servers, each shedding 300 watts of heat annually, a total of 600 megawatts. These are linked to hard drives that dissipate perhaps another gigawatt. Fifty percent again as much power is required to cool this searing heat, for a total of 2.4 gigawatts. With a third of the incoming power already lost to the grid's inefficiencies, and half of what's left lost to power supplies, transformers, and converters, the total of electricity consumed by major search engines in 2006 approaches 5 gigawatts.

The article continues . . .

PC power supplies are said to waste over a third of the energy they consume. Google claims to have technology that reduces waste to 10% and offered to share it during a presentation at yesterday's Intel Developers Conference.
Surprisingly little coverage of this in the US media, but I found a good report from the UK print media.