I've nearly gone as far as I can automating systems and devices my current home - temperature & humidity sensing in most rooms, motion sensing in every room, zoned ducted evaporative aircon, a couple of split reverse cycle aircons, z-wave lighting and exhaust fans, and mains power monitoring.
-- Lighting ---
Z-Wave works mostly well enough, and I use this to automatically turn on lights when motion is detected, turn off lights after a while with no motion, or turn off when I go to bed. Unfortunately the turn-on the signal can take up to several seconds on a large 1-wire network, so even when the motion sensor triggers quickly you can still be halfway across a room before the lights turn on which is a pain. On top of that, I cant disable the z-wave dimmer soft-on and soft-off feature which is a pain when you're trying to get quick response. For the turn off, it's probably not worth it since I upgraded to LED lights as the power saved is negligible.
At the price of parts + install being $150 - $200 per light fixture it's not really been worth. A few minor conveniences and a lot of annoyances. I think I'd be better off with no automation on most regular light fixtures, and just some inline z-wave switches on frestanding lamps and mood lighting. Maybe automation on the living room and master bedroom for convenience / scenes.
-- Temperature / Humidity ---
Temperature and humidity sensing in every room has been great. In Australia where I live it's quite uncommon to have a whole house climate control system, so I've used these to help come up with a automated strategy for every room that integrates the available air conditioning systems. Also I've used the temperature, humidity and (calculated) air speed in each room to create a "feels like" temperature. Controlling against this rather than the dry air temp has given a much better result.
I've been using 1-wire devices as sensors, which need 1 or 2 twisted pairs for comms and power - cat5 is great. The DS18B20 temperature sensors are very cheap, have been very reliable and can send signals over long distances. Unfortunately the DS2438 based humidity sensors are not as good and I've had to partition the network a 1-Wire hub. Currently I still have intermittent errors with just 30m of cable on each DS2438 leg, whereas the DS18B20 temperature sensors could cope with a load of 100m plus. If I was building a new house I'm not sure if I'd use them again due to the issues with humidity sensing, but I'm not convinced there's many other affordable alternatives either. For reference the DS18B20 sensors are costing me about $2 each, and the DS2438 based humidity sensors (using a Honeywell humidity IC) are about $20 each from parts. Since I work as a control engineer, my next preferred option would be modbus slave devices over RS485.
-- Air conditioning ---
For the split reverse cycle aircons I used a central GlobalCache IP2IR infrared blaster, and then ran long wires with a concealed IR emmitter fitted inside the aircon head units. This works fine but the IR programming for air conditioners is painful. I wish there was an automation interface standard for them.
For the ducted aircon I had to integrate the zone controller using an arduino for digital IO, communicating back to the central server via RS232 serial (over cat5). I upgraded the fan to use a VFD (variable frequency drive) and this can be controlled directly over RS485 using MODBUS RTU.
-- Conclusion --
If I had my chance again I'd probably just run multiple cat5e or cat6 to every room
- 2 to 4 at floor level for computers and TV's
- 1 or 2 behind the light switches for potential CBUS or other wired lighting control systems. These would be wired to a seperate patch panel
- 1 or 2 behind a wall mounted sensor enclosure - this could then have both a temp/humidity sensor and IR emitter fitted. These would also be wired to a seperate patch panel
Ideally I wouldnt run any mains power to wall light switches - all of the switching would happen over serial comms or low voltage IO (using the cat5) and then the mains switching can happen centrally - either dumb relays, a PLC or CBUS controller.
The above setup would then make interconnect and automation via either Ethernet or serial (RS485) easy, both of which are reliable and well supported protocols. RS485 doesnt get much attention in home markets but it's still huge in industry and commercial installs.