My home is fairly small (less than 1000 ft2) and does not contain many lights or outlets (much to my chagrin). Not many switches are needed to control the lights and I'm disinclined to replace much, if any, recepticals. The principal devices I would like controlled/reported are overhead lights, fans (which proves difficult since they are are not seperately switched from lights), the thermostat, and tie into the now-defunct security system. I'm also considering replacing my locks with compatible electronic ones.
Almost as important as control is reporting. I want to generate a parsable log file so I can generate graphs of light/appliance usage, see when doors were opened and closed, and how often and for how long the thermostat ran.
For light control I've considered x10 because of the cheap cost of modules (often less than $10 for a box or swtich) but have suffered greatly at how unreliable it is. I'm now deciding between Insteon (for which x10 is compatible, and I already have a computer-insteon interface) and Z-wave. As of writing this, I'm leaning towards insteon because it seems to be reliable and is cheaper than Z-wave.
As much as I like the idea of building my own thermostat, I have discovered a thermostat by Insteon that would suit my needs. It probably would cost about the same to build my own thermostat as to buy the Insteon one and the Insteon one will be of no doubt high build quality.
The house came with a security system installed. As far as I can tell there are only door sensors and and a siren installed. The door sensors are simple magnetic sensors that provide great resistance in one state and allow current to flow in the other state (I forget which is open and which is closed).
I plan on integrating the doorbells into the security system aspect.