I'm not drawing any lessons other than maybe "there can be only one winner when there is no clear revenue model."
Brightkite had geotagged photo uploading and an iOS app before Foursquare even existed. But they exited / acquihired while Gowalla and Foursquare were just ramping up. So it goes.
Last I checked their active users had flat lined, AFAICT,Foursquare is going to have the same exit as Gowalla, possibly with the exception of riches to the founders and every one else left hold the bag.
Brightkite had geotagged photo uploading and an iOS app before Foursquare even existed. But they exited / acquihired while Gowalla and Foursquare were just ramping up. So it goes.