Mapnificent (http://www.mapnificent.net/ http://www.mapnificent.net/) does something like this and even has an API. I started writing a Chrome extension using

Mapnificent (http://www.mapnificent.net/ http://www.mapnificent.net/) does something like this and even has an API. I started writing a Chrome extension using the API that you could apply to any existing Google Maps v3 map (such as AirBnB), but I've abandoned it since 1) I was disappointed that quite a few sites with Google maps are still using older versions (such as Padmapper) and 2) I lack time. I believe the Chrome extension portion is working, but it needs a UI overlayed on the map for specifying locations of interest. If anyone is interested in working on this, send me a message and I'll post what I have to github.