Warren Meyer has a great idea on a way to make money wiring homes with 12v DC:
But as much as I hate CFL's, I am coming to love LED-based lights. LED lights use even less energy than CFL's and last a really long time. The technology allows for color tweaking better than CFL's, and already the warm white LED's I am buying (color temperatures around 2900K) are better to my eye than CFL's, and there is no fast-flicker problem that gives some people headaches. Dimable versions are coming out, and prices are dropping but they are still expensive. About half my house is LED now, and I am told that landscape lighting is quickly going all LED.
The main cost to LED's is that they all have to have a transformer. LED's run at low voltages, like 5v, so house current has to be stepped down at every bulb. LED's in theory should run cool and be cheap, but they are expensive and run hot because of the transformers.
Which leads me to wonder whether we may start wiring houses for 12v in parallel to 110v. When I grew up, nearly everything I plugged into the wall -- lights, motors, appliances -- ran on 110V. Now, most everything (other than appliances) that I plug in the wall actually needs 5-12v (computers, cell phones, all my audio equipment except big amps). I don't know enough about power lines to know if this is feasible. I am pretty sure the resistance losses for 12V DC would be too high, so it would have to be 12V AC, but a diode bridge and some capacitors is a hell of a lot smaller and cheaper than a full blown transformer. I know my landscape lighting has long runs of 12V, that seems to work OK. It is also a hell of a lot safer to work with.