Steve Wozniak, of Apple fame, is jumping on the green bandwagon in a big way. He's discovered the idea of building homes that require little or no power to heat. Some of his ideas are a little misguided (eg, he suggested in an interview that one should knock down energy inefficient housing and replace it with shiney efficient housing - neatly ignoring the aount of energy required to build a home, not to mention the landfill required to dispose of the old one), but it's excellent that someone in his position has publicly declared energy efficiency to be a Good Thing&tm;, particularly as there is a certain class of Apple customer who will do everything the Steves tell them to :-)
One facinating idea he's come across (and no doubt will invest in) is that of using a particular wood for your core building material. Southern Yellow pine has sap that melts at about 22C, so as the external temperature rises above that, an enormous amount of energy is absorbed by the wood to melt the pine - keeping the internal temperature down. Neat idea - there's a few complications that I see - eg, sap tends to dry out over time, so it may lose effectiveness over time. Also, many people are allergic to pine sap, and as it evaporates (which surely it must if it becomes liquid) the house is going to be infused with vapourised sap. Not so good. Perhaps a synthetic version could be produced, with the working fluid sealed inside the structure of the building.