Just installed an ecobee smart thermostat. Had Nest in my last house so wanted to see how the two compare. On first impressions ecobee is edging it already, and when I start getting into the interop functions with other tools I suspect it will become a bigger margin.
If you don't have a smart thermostat you should get one. They're awesome, they save you money, and they're so simple that even MBGreen could install one.