From my story on Facebook location back in March:

One person who has seen it notes that the icon for the location feature has a pushpin on a map. This was apparently a beta version of an app, but the functionality, if Facebook chooses to go with it, would likely be built into the massively popular Facebook iPhone app.

And word was it was using both Gowalla and Foursquare check-ins to populate the area. All turned out to be true.