From a Popular Mechanics long term gadget review:

The premise of the Nest system is an efficient home-climate-control system that you don’t need to think about. But in three months of my experience, the exact opposite is true. Because the device is constantly and autonomously tinkering with the temperature in my house, I find myself frequently checking in on it and second-guessing its intentions. When I hear the heat kick on, I run to the Nest and examine its current setting. Do I really want the temperature to dial up to 72 degrees F? Now I’m not sure.

Other Links:

http://www.popularmechanics.com/technology/gadgets/reviews/nest-thermost...