There is so much potential for geo-fencing. I'm currently trying to figure out how to use it for a one-time scavenger hunt, with no luck in figuring out the tech. A service for this would be worth money, certainly.
The vision is being able to say "Give me all of the bits of geodata my friends have left on any service" with a single call.
We are going to provide hooks for data and identity providers to tie into our platform.
Would you be interested in something like this, and what would you want out of it?
We've been considering that as a demo app for the platform. The initial idea was just to mark a point and a radius for a chat room, then when users enter the area they'd get a notice pushed to the phone like "geochat app has a chat room here. want to join? [yes/no]". The app developer would use our api to tie a (lat,long,radius) to an action (geochat-app/load-chat/{chat-id}, for example). Combined with our own app that monitors user location, we can run the appropriate action for the (lat,long,radius,app,user) set and launch the developer's app.
A specific bounding box instead of a radius is a good idea, and we'll add that to our to-do list.
Would something like this be useful to you?