CANNOT CURRENTLY BE INTEGRATED. Just saw on the C4 forum that a C4 dealer approached Nest about control. Their reply: "Thank you for contacting nest. The API or SDK is not available at this time."
One other thing that I don't like. It's learning process is based on when you turn the dial (not affected by you changing the schedule via wifi). So, for me to teach it to turn the heat up on cold mornings so the house is warm WHEN i get out of bed, I need to get up earlier, turn the *$@%$ thermostat ring, hop back in bed to warm up, then get up at the regular time when the house is warm. That's screwy, to say the very least, when I can program my thermostat to do that based on time, or with a HA system, adjust the programming without worrying about a "learning" device changing it on me. Likewise, I want it to be cool (or warm) when I get home, not 30 minutes AFTER I get home. So I have leave work early for a week or more to train this *$@#$% thing? I know you can adjust it remotely, but that's different from it "learning". Maybe I'm just missing the point of this device.
This will fit the iDevice crowd just fine and sell wildly because of it. Those who want true HA will go with devices designed specifically for HA.
WHOA: Just looked at the price. . .No thank you. My little programmable thermostat does just fine.