If you are in the data center business, get to know PUE: Power Usage Efficiency. PUE is a measure of how much additional electrical power is needed for cooling to deliver computing power. A PUE of 1 means all power being used for computing and none for cooling.
A 2007 US EPA survey put the PUE for your average data center at 2.
On the other hand, Google claims a PUE of less than 1.21 for six large scale Google-designed data centers.
Now vendors are responding to the need with self-contained low PUE computing systems packaged in shipping-style containers. SUN was first with their MD S20 with 280 pizza servers in one container, while the Verari Systems solution has 1400 blade servers.
Very large low PUE data centers such as required by Google, Microsoft and Yahoo! can be built by deploying warehouses with potentially hundreds or even thousands of these containers. In fact, that's happening today.