Geo-thermal heating

At least I think thats what its called - I'm going to start building my new house next year and am looking into geothermal heating - the one where you lay coils of piping under the ground where its a constant 10 degrees and this in turn is converted into enough heat to heat your house and water. Does anyone know anything about this? I know its more expensive than installing ordinary oil heating but with the price of oil it willobviously/hopefully be cheaper to do this in the long term. I also know that it works best with underfloor heating which is what we intend to have. Does anyone have any experience of this type of heating? Costs/pros/cons etc.

Thanks