I bought a Nest learning thermostat.
Having read about the Nest for months and hearing rave reviews I finally broke down to peer pressure and bought one.
Er, I bought three.
Yes, sad to say, I have three air conditioning compressors and three furnaces and three fan systems operating upstairs, downstairs and in the Master Bedroom suite which is as large as a small country.
So far, so good. The Nest was dead easy to install although the touch-up needed around the old thermostat will take some time to do, and probably result in painting the entire interior of the house.
The Nest should pay for itself in less than a year in energy savings, although the interior painting will push out the recovery period about 2000 years.
Ah, so. It is cool!