Gilles Barbier pointed me to his geo-localized application using Google Maps: Tellmewhere (dis moi ou). This site is basically a geo-wiki where everybody can describe collaboratively what they know on earth! They are currently focused on France, but they plan to expand quickly after opening. This service is a sort of hyper-local site: they are going to add some social tools to help people of the same neighborhood to realize they share the same places.
I really likes the interaction. The reviews of the locations are quite detailed, it is possible to add pictures, and it allows social ratings on the posts. Really nice!