A local car service is the mayor of LaGuardia Airport in New York. How long will it be until Foursquare begins selling space here to advertisers? This is the first page you see after checking into a business — and I have to imagine it helps deliver new customers to this car service. Imagine landing on the runway, opening your phone and checking into 4sq, and clicking a link to schedule a luxury car service drive you home for the same price as a taxi. Not bad.