This is a rather unusual idea and could make its way: Home Elephant is a social network with your neighborhood.
Its applications are various : to know a little more your neighbors, organizing partys and events, ask a question about garbage collection (when is it already ?), an alert in case of theft, loss of pet, a removal, road construction, etc..
Basically it is a private network that adds a layer of security at home, in addition to having all the answers about what happens next to your house.
Currently in beta, the site has already 2600 neighborhoods in 38 countries.
It works via a mobile app with Android, iPhone/iPad, and as a Facebook application.
Demo videos and ads :