Read this article today. IBM is looking at using heat from data centres to warm homes. There are a few data centres in Singapore. Fujitsu has 3 data centres in Singapore (Ayer Rajah, Tampines and Changi). The 3rd one opened in Feb 2009 and cost S$ 15 million and designed to be energy-efficient (according to Fujitsu). With Singapore already being so hot, I really can't think of how that extra heat can come in handy. If you are interested, you can download Amory Lovins (Cofounder, Chairman and Chief Scientist of the Rocky Mountain Institute (RMI), a leading institute in energy efficiency) seminar on energy efficiency in buildings and data centres in Singapore.
Some countries actually put their data centres underground. Besides energy saving (constant and lower temp & ground water can be used as a coolant), going underground offers additional security too. Examples, include Kansas City, US, Sweden, and Japan.
Hmmm... sounds like a good idea, but I'm not sure about working underground. It looks claustrophobic!