While programmable thermostats are nice, imagine what you can do with one that can respond to situations!
New technologies have brought robust HVAC control to the automation world by simply replacing the thermostat. Aside from setting simple times and temperatures, you can now make the system respond to your lifestyle. Press an AWAY button when you leave to turn the system up a few degrees while you're gone. When you return, press HOME and the settings are instantly restored. Use the thermostat to report house temperatures to your automation server so that it can kick ceiling fans on before the actual need for air conditioning. In businesses, you can have the system shut down after hours.