What you need to know about Foursquare
Update: a more nuanced look Foursquare from Charles Arthur, Russell Davies and John Willshire, an interesting experiement from Harvard using Foursquare and one from Bravo on a seemingly much larger scale, and here in the UK, news from Marketing of Debenhams and Domino’s Pizza use of Foursquare.
Update 2: Ten Foursquare marketing campaigns.