Surprised to see that it has now raised a total of $106 million.
What are you talking about? Foursquare ain't getting anything for free, if anything that debt is now over $50m at a very conservative 15% Kd assumption.
Here's a presentation given at Data Driven New York. http://vimeo.com/79911529
Location data changes very quickly: new places open and close, popularity waxes and wanes, and demographics of neighborhoods change unpredictably. Foursquare's location data is only as good as its freshness, so without a large pool of active users, there is no "data exhaust".
But it did sound like check in growth was tapering.