I was going to get a Nest a while ago and ended up not getting it. Bunch of super bad reviews on Amazon and other places. Basically they said that the Nest would not remember settings if it lost power and can cause freezing issues in the winter if it occurs at the right time, some ppl saying it trips out often and just runs super hot heat uncontrollably, some ppl saying it trips out and runs AC and Heat simultaneously. Nest actually responded to some of these reviews and said that they recognize the problem and were working on it for the next Gen.
Also, some of the reviews were by service tech types saying they love the Nest because it keeps them busy and getting paid.
I don't have one, but just seems like a lot of neg response.
They sound awesome if none of the above is true.