I find geo-location based services to be quite fascinating. Windows 7 brought with it themes and geo-location sesnor APIs, mixing both to have themes change based on geo location has been lingering on in my mind for long. Once Long and Rafael released Geosense, I realized this could quite well be possible without depending on GPS hardware.

I call this application GeoThemes. The idea is quite simple,  you can set themes for specific locations, a different theme for work or college and a different one for your residence. A simple mock up of the application: