Facebook Map of the World
This map is very cool.
This visual representation of the connectedness of the world as viewed through a subset of Facebook friendships looks surprisingly like the international flight route maps found in in-flight magazines.
The great circle representation of the connections certainly contributes to this impression, but I'm guessing the strength of the signal for connections at air travel hubs is at least somehow related to the in-person connections that have been formed via air-travel.
His blog post explains his methodology.