My house has a rather extensive array of X10 devices - every light is controlled by X10, I use motion detectors to turn on the bathroom lights and speakers when someone enters and to turn on the exhaust fan when someone goes in the shower.
I use a Stargate to turn on/off lights at different intensities depending on the time of day, sunrise/sunset, or whether someone is home.
And I plan to do a lot more, such as have a drip pan made to go under the hot water heater and use a moisture detector so the system can alert me the next time the hot water heater fails (it is in the house).
I am rather happy with the system, but if I were building a new house, I would sure investigate hard wired systems and/or CEBUS which also sends signals over the power line but is more advanced - it has collision avoidance plus other features.
I expect any of the systems that I suggest are more expensive than X10, but if you are going to do very much with X10 and use the better components (the ones not made by X10 Powerhouse), the investment can be sizable - at least by my standards.
You might find some interesting info at http://www.hometoys.com