Change background based on location/wifi? Does anyone know if an application that can change the background of the desktop to a different set of images based on your location?

I am thinking about writing an AppleScript to do this, but if someone knows an application / script that already does this that would be great?

I want it to check every time I login to the computer and it would be great if it could do the 1 hour rotation that I currently have, but otherwise a random image from a folder each time I login would be fine too.
Anything involving location-aware contexts can be done with Marco Polo.