Over the past three years i've upgraded my thermostat from the 7 day programmable to a 7 day 'wifi' programmable to an ecobee3 and I honestly can't see any savings on the utility bills from the basic one. The first two were both Honeywell thermostats, and it was frustratingly difficult to keep the online version connected and ended up with the ecobee3.
I have to hand it to ecobee for having a lot of configurable options and additional sensors you can toss in a few rooms but it's still very quirky. From day one, the sensors randomly disconnect, you can go for weeks or months without an issue then all of a sudden you have several emails, phone notices, app notices, thermostat notices all at once. Like Honeywell's crap, you get the occasional random disconnect and you have to re-login to get things to work but at least for ecobee, it only takes a few seconds. The geo-fencing feature is probably the least reliable system i've seen and is made worse when connected to Apple's homekit. I believe the key problem is that you have to have a reliable cell connection as you enter and exit the defined radius, clearly an issue for me with non-flat landscape which can cause spotty cell coverage.
I will say this is that when the additional room temperature sensors are working and the added feature to run the fans for a minimum duration an hour the entire house is noticeably more comfortable. I even have it configured to run the AC to adjust the humidity as needed, but it doesn't really get dry enough in my region to really need that. I do like the fact that I can remotely change the temp, so for that extremely rare emergency with enough days away, that might actually save some money.
I'm curious if anyone with a smart thermostat has experience any real savings? I don't think I will ever recoup the cost of the thermostats themselves, but assuming they last a good ten years, then I would consider it worth it.