Google blog posted an update about the efficiency of Google data centers:

[…]In Q4 our average power and cooling overhead in these facilities was 16%, bringing the overhead for the trailing 12 months to 19% (down from 21% a quarter earlier). For comparison, a recent EPA report put the overhead of the average enterprise data center at 100% or higher. We're very happy to have further improved our efficiency, and a number of factors contributed to that result.[…]

Full Article