I have a nest, and this is what I think.
Firstly, I was given it, I don't think I'd ever have bought it.
1)Multiple temperature setting events per day.
For instance 05:50: 20 degrees, 07:00, 9 degrees, etc. I've not found a limit on the number yet.
2) Looks nice
3) Interesting to see when the heating was on for the last 10 days
4) Ability to turn on remotely when I know the kids are in (but upstairs) and its turned off. However this wouldn't be needed without Dislike (7).
1) Learning facility is useless.
2) Remote control is a useless gimmick. Never used beyond the first few weeks.
3) Software errors cause unexpected heating schedules
4) Software updates cause unexpected heating schedules.
5) "True radiant" (where it turns on and off early) is useless.
6) Annoying that I cant see when the heating was on since I installed it.
7) Auto away that turns heating off when people are in the house but not passing the thermostat.
8) Price (Although mine was free).