A "Places" plugin would be very useful for a social network.  Like in FB, users would be able to "check in" at places.  If the place does not exist, they can create it and classify it under pre-defined categories.  This would be a great place to find others that frequent the same place and happen to be in the same social network; let friends know when you are at a place; or let them know of the place.

Integration into the Events and Extended Events plugin would also be ideal.