According to DOE in 2006 computing facilities consumed 1.5% of the electricity in the USA. Large computer facilities currently are set up in such a way that a room packed with servers is serviced by a large air conditioning setup. The room is setup in such a way to try and minimize the air conditioning costs. The servers are setup in a pattern of alternating hot and cold aisles and I have seen in some cases where ceiling baffles have been installed to encourage the hot air to rise into AC intakes instead of being displaced into the cold aisles. These same setup usually have special covers to attempt to prevent the loss of cold air through cable conduit and power outlets, as with the incredible number of such connections they account for a large surface area.
After some thought I realized that perhaps a better way to deal with this sort of a computing facility would be to switch to liquid cooled systems. Liquid cooling is used by gamers on high end gaming PCs which are often overclocked to the point that conventional fan based cooling can not provide sufficient cooling to keep them functional. Currently liquid cooled PCs are available or can be built from parts but are for the most part all custom. Online retailers such as Frozen CPU will sell the parts necessary to convert a regular PC fan based system to a liquid cooled system. A direct conversion would not work for a large computing center as the heat would need to be moved outside of a building but if the manufacturer of the blade centers included a liquid cooling option on the blades with a with some ability to combine these into a single radiator or cooling pond based solution might be more energy effidient than standard heat exchange systems. Searching the internet shows that there is some work in this direction. IBM offers their Cool Blue technology which uses water cooling on the air flow through the server. This setup is ideal as it can be added to any server but is still partially an air cooled setup.
Currently this is just a theory that this may be a better way to cool a data center. Direct calculation of the amount of energy used to pump water and cool it outside a building would seem to vary a lot depending on circumstances. In some regions this may also be an inappropriate way to cool computers as water may be scarce in that region. In order to determine if this is actually a better way to cool a PC, in terms of energy efficiency, someone with a PC they could convert to water cooled or fan cooled and some method to measure energy consumed and heat generated would need to carry out an experiment comparing the two systems.