Okay, to the Car+ Building posts below, add the thought that plug in hybrids (or electric cars), could act as a buffers to the electrical grid, giving it a place to store surplus power, and then to draw that power to respond to surges or increases in demand. This buffering service could reduce our need for the most expensive, and dirtiest "peaker" power plants, and make the intermittency of wind and solar less of an issue. What's more, vehicle owners might be paid for the buffering service (in addition to the deep discount on their motoring energy costs). See this NewScientistTech article or some thoughts on V2G (vehicle to grid) from the Rocky Mountain Institute.
A little dowry for the building/car marriage.