Have one and like it. I haven't noticed any savings on my bills. In fact, they seem higher. Why do I like it then? First, you can control the thermostat with your smartphone. That means you can turn it on, off and adjust the timings of certain things. I also like the fact that you can have the fan turn on and off instead of the a/c or heat. This is useful to just move the air around. I like the fact that you can very easily adjust the time and date settings on line or on your smart phone. It is very easy to do. I work from home some days and not others and this is easy to adjust. I like the fact that it turns off if we are not around and goes into energy savings mode. Finally, it is super simple to install. Not that installing a thermostat is hard, but the Nest comes with stickers, screwdriver, etc. and is easy to connect to your wireless connection.
Is it worth the money? I don't know, like I said we haven't seen a costs savings. However, we needed a new thermostat and the Nest was about 100 dollars more than a comparable thermostat. If I were to do it again, I would make the same choice.