Thermostat Control Based on Location and Weather
Hans Scharler has designed an automatic thermostat for his house that uses Google Latitude, WeatherBug, and ioBridge to control his heating based on his location and the weather.
Using Google Latitude on his Android phone Hans is able to control his thermostat automatically when he leaves his house or when he is coming home. Leaving home is relatively easy. Using Google Latitude his 'Location Aware Home Automation' system can turn off or enter power saving modes when it detects he is away from his house.
When he is returning home the system checks the weather using the Google Weather API and the WeatherBug API, and then checks his home temperature (via ioBridge) to see if the house needs to turn on the air conditioner, the heater, or neither.
If you want to try and replicate this Hans explained how he put this together on his I am Shadowlord blog.