Buried in this article on the Nest acquisition is this little gem:
Researchers in 2011 were even able to use a similar approach to determine what movie was being watched on a television set by making energy profiles of each film. This was achieved by observing that a television’s electricity load will vary over time depending on whether dark or light scenes are being displayed to the viewer.
Although the researchers in question relied on very granular data from the television set, Danezis worries that such techniques could one day offer smart-home companies an X-ray view of your home.
Here’s a link the research. Basically, they used an energy profile to determine what you were actually watching.
To me, that’s the real value of this Nest deal for Google. Google has so much to learn about you and your habits, and this is their first foray beyond the screen. The Nest thermostat learns about when you leave your home, when you are home for extended periods, etc. The name of this game is extrapolation. Are you suddenly home for extended periods? Does this mean you lost your job? Perhaps some nice help wanted ads on your refrigerator would be appropriate.