Until now, the Nest Thermostat integration was focused on turning heat or AC on/off when a tag that monitors temperature reports "too cold", "too hot" or "back to normal".

We also receive current temperature and humidity updates from the thermostat and save it for historical graphs (up to 10 days per Nest policy). The temperature update allows triggering "too cold", "too hot" or "back to normal" events and KumoApp event handlers assigned to "temperatureChange" or "temperatureCross". This means if you have another WiFi thermostat including ones from Honeywell, you can choose your Nest Thermostat as if it is a temperature sensor tag in the "Set At" option to make it turn on/off another thermostat.

Nest Thermostats contain sophisticated algorithms to use sensor (a PIR?) and scheduling to determine if the house is occupied or not (i.e. "home" or "away"). Nest encourages developers to use this information in an integration. 

Starting today, the Nest thermostat "tag" will generate "Detected Movement" (i.e. transition from "away" to "home") and "Timed Out" (i.e. transition from "home" to "away") events just like a PIR KumoSensor. You will also be able to assign KumoApp event handlers to "detected" and "timedOut" of the Nest Thermostat to perform actions like arming or disarming motion sensor tags, as well as use corresponding IFTTT WirelessTag channel triggers. 

From the Web/Android interface you can click the ">" button to open a PIR sensor-like notification option screen for your Nest where you can choose emails, twitter account, push notification sounds for these events. 

Also, now if you have configured the "Set At" for your Nest such that HVAC is triggered by a wireless tag, when your Nest transitions to "away", temperature monitoring of the tag will be automatically disabled (so it will not try to turn on HVAC when nest is in "away" mode), and when Nest transitions to "home" the temperature monitoring at the tag will be re-enabled. This is actually a feature a lot of people wanted and long overdue.