The folks at Contagious Magazine have an interesting piece on visualizing check-in data. Weeplaces.com lets you visualize your check-in data across several services, including Foursquare and Facebook Places. I generated mine fairly easily.
This reminds me of nothing as much as Plazes, an early check-in competitor (that relied on MAC addresses to “claim” locations — this was pre-iPhone, of course.) Plazes caught on a bit, and was eventually bought by Nokia, but lacked the critical mass needed for applications like Foursquare, Groupon, and Gowalla.