More like a parasite/host relationship, perhaps, than an integration Gowalla catches a ride on competitor Foursquare. Sort of. Read the full article at Mashable for the juice.
Gowalla Turns the Tables, Integrates With Foursquare
Gowalla did not work with Foursquare on this integration; it was all done through the API. That leaves the real possibility that Foursquare could throw a big wrench into Gowalla’s plans by blocking its rival’s use of the API. The threat posed by Gowalla 3 is real; that alone could force Foursquare’s hand in the name of competition. It would also create a firestorm of controversy.