I've had a Nest thermo for about a year. For me the #1 thing about it was the smartphone app - in particular the ability to tell it to turn on the heat if we were coming home earlier than normal (or the opposite). Our radiators take a while to warm up the house and this allowed me to keep the house fairly cold when we weren't there w/o any discomfort when we came home.
That said I was disappointed with its learning capabilities in terms of our schedule. Sure, it picked up on trends but it just started slapping temperature change event on the schedule instead of adjusting things. So what happened was that it would get a couple of pinch points where it'd set to 65 at 10, 67 at 10:02, 66 at 10:05, 68 at 10:10, etc and I ended up cleaning it all out by hand anyways. It'd have been nice if it recognized we probably wanted it around 66-67 around 10:05 for instance.
That said I was disappointed with its learning capabilities in terms of our schedule. Sure, it picked up on trends but it just started slapping temperature change event on the schedule instead of adjusting things. So what happened was that it would get a couple of pinch points where it'd set to 65 at 10, 67 at 10:02, 66 at 10:05, 68 at 10:10, etc and I ended up cleaning it all out by hand anyways. It'd have been nice if it recognized we probably wanted it around 66-67 around 10:05 for instance.