Interesting

A very good post on GeoThermal energy by Malcolm Gladwell. For a simple explanation as to what it is

Geothermal heating and cooling is based on one simple fact: that 6 feet down in the ground the temperature is the same—between 50˚F and 60˚F- the whole year round. This means that it is relatively cool in the summer, and relatively warm in the winter.
...
For geothermal cooling, all one needs to do is to circulate water in a pipe through the ground to cool it, and use this cool water to cool the air pumped through the house in the heating ducts.

Heating is done much the same way. The numbers seem quite plausible, I wonder why it's not more popular.