Regardless of the need to have it for X10 modules I think you will find that the national electric code and your local electrical code will require 12-2 with ground for outlets, minimum of 14-2 with ground for lighting. You may also want to consider if your going to have any 3-way switches that you run the 12-3 with ground between the switch boxes. This way if you ever move and pull the X10 out you could install standard electrical outlets, switches and 3-ways if need be. Also look at the need to run phone cable, cat 5 network cable and maybe any extra cables for cameras.