Oh, I've been chomping at the bit for geothermal heating/cooling for almost a decade and a half. In Oregon, it's mild enough that retrofitting the house for it would cost more than it would save for a very long time. If I were to build the house from the ground up, though, I'd start off with geothermal right away.

Yeah, geothermal with solar panels and a wind turbine... *dreamy sigh*