BART will award $25 promotional tickets each month for the next three months to riders chosen at random from all the riders who have logged Foursquare check-ins at BART stations, starting in November.
Foursquare will also supply a BART "badge" for frequent riders who checkin to the 43 stations around the bay area. BART is taking advantage of the Tips section of Foursquare by listing popular venues and things to do around BART stations as well.
This is a genius move by both BART and Foursquare because neither party really has to do anything except watch the social web. Don't be surprised if Foursquare inks more deals like this with local companies.