Most of the few routines we have in my house involve the thermostat - at night, as we all trek upstairs to bed, I turn the main floor thermostat down and turn the upstairs thermostat up. In the morning, we do the reverse. It keeps our heating bill down, but it's a little like trying to save gas by hypermiling - not everyone is going to put in that much time to save a buck here and there.
The Nest "smart thermostat" might fill a need for people who want to keep energy use/costs down without spending a whole lot of time monitoring the in-house temperature. It learns your preferences over time, by watching how you high you set the thermostat and taking temperature and humidity data through wi-fi. You get the cost savings of energy "hypermiling" without having to do the work yourself.
The drawbacks? For one, it costs $250, although that might pay for itself if you really end up saving money on the heat. And a lot of smart meter-y things have failed to catch on with consumers. Maybe smart device companies need people to buy a smart device that keeps track of smart devices they could buy to save money? Nah, that's getting a little meta.