There have been instances of small bars and restaurants giving discounts to the Foursquare user with the most visits to the establishments (called the Mayor in Foursquare jargon). This, however, is the first real example of a national business offering discounts on such a scale. Starting now, and running through June 28th, the mayor of any particular Starbucks location will get a $1 discount on a Frappucino there.
Starbucks seems to have embraced the social game where users check-in as they go about their business, racking up points and getting badges for completing achievements. The coffee chain previously created a "Barista badge" for Foursquare users. This promotion isn't interesting because it's such a great deal, but because it shows companies are beginning to see the advantages these social games can have in marketing.
Are you a Foursquare user? If so, what sort of product tie-ins do you think would work?