Pull in someone’s friends on Gowalla, Foursquare, Twitter, Facebook (anywhere that makes sense) and show them a single view that displays where their friends are right now.  The activity stream on Gowalla will show you recently what some of your Gowalla friends have done, but this may be more than you want (not all my Gowalla friends do I really want this level of detail on), and also it does not answer the question, where is my friend Bob right now or where was Bob last seen?

Ideally, there would be a search box to find your friends last location quickly, a listing of locations, and a map of your local area showing friends.   The Gowalla iPad app gives a sense of this but again, I may not really care about all these people at that level, so there should be ways to turn on and off who I am seeing.