Goolge Plus has an impressive nearby feature. So you can navigate posts to G+ not only by who is in your circle, or what is popular, but also by what is being posted near where you live. This is an impressive simple way to harvest geo-location data to view the feelings and interests of the local community, even if local is the other side of a big city like London.
Facebook allows you to see where fellow users have checked in, but the feature is underused and I have found it had no real value for me.
Perhaps the best use we have seen of geo-location is the Flixster App, which support integrations with Netflix and Facebook accounts. It also feeds data from Rotten Tomatores. The app adds geo-aware, so it can tell you what movies are playing near you, then give you the Rotten Tomatoe scores, your friends ratings, and even download a trailer on to your app. Flixster makes finding a local movie you can walk to more like downloading from iTunes. We love these class of apps that make social and community engagement as easy as non-engagement. You can find a theatre to see a movie in as easily as you can download a movie on iTunes.