Much to the irritation of many users both Foursquare and Facebook have split their apps into separate tools.
Fred Wilson of Union Square Ventures, one of the investors in Foursquare, explains the reason for this are that different patterns meant the service had to cater for privacy models which threatened to confuse users.
The risk for both Facebook and Foursquare is that irritated users might give up on the service, it’s a tough balancing act.