We could actually see the appeal of the app to a company like American Express, which caters to certain clients. With Foursquare alerting users to certain eateries, it could also be a great tool to lead the app's users directly to those restaurants that accept American Express. And since Foursquare users are more apt to eat out and shop, they are the perfect demographic to advertise AMEX credit cards to. Foursquare recently started a new service that allows brands to advertise directly to users once they have checked into a location. When you think of Foursquare, think of targeted advertising.
For Microsoft, a stake in Foursquare would give it a larger investment in social media, an area where it has trailed competitors like Apple. The Redmond based software giant has a great track record in social media investing as it took a stake in Facebook back in 2007, making a fortune. But Foursquare is a small company that rang up just $2 million in sales last year. Its new ads are clicked on or saved after check-ins more than 15% of the time. That crushes the average 1% click through rate on mobile ads and makes Foursquare a very desirable advertising option.
American Express wouldn't comment on the rumor, saying that they never respond to speculation. Microsoft responded in a similar fashion.