Imagine visiting Washington D.C. As you walk around the city (not recommended today, as it's over 100 degrees...) an application like Foursquare offers tidbits about movies that were shot on location at the tourist attraction where you're standing.
"In a perfect world... location-based social networks would act like browsers, able to see and post interoperable location-based data from and to any platform."
Even though there's a lot of technical work that would need to be done to make this idea a reality, it's exciting.
Foursquare Launches Location Layers