After doing some research on the Nest, it seems that it does make it more comfortable, but it never received the Energy Star award. Seems to do the opposite. Of course you could turn off your a/c or heat when you are gone, but it turns on when you aren't home, and you have to manually over ride it.
Seems like you realllly have to tweak it. Also, I noticed the reviews on the Amazon and there are quite a few mixed reviews.
TL;DR - I'll wait for cheaper pricing and more testing.