"In regards to location-based applications, Foursquare CEO Dennis Crowley talked about how the app is becoming more passive, and hinted at kicking check-ins to the curb. Crowley said that the company is moving away from check-ins to focus more on the Radar feature, which collects information about where you are, what direction you're going and lets you know when you're close to places on your lists." - from here
I think there are simply much more users in Facebook. So what is the point check-in in Foursquare and translate that record to Facebook where all your friends are. You can check-in via Facebook directly. And FB has got a huge base of places.
/via QRpon - customized check-ins for Facebook