There is a nearby friends map, but it only works for people who have consented for Facebook to track their location 24/7.
I've played around with building an app that uses the Facebook API (and other social networks) to get people's current "Lives in" city, and location updates from recent posts, and aggregate them all in a map. I found it a bit hard to get this information from the APIs, and never had the time to figure out how to get it to work.
