Check-In Counter

How hot is the location services market right now? Ask Foursquare’s founders, Dennis Crowley and Naveen Selvadurai, who are splashed in magazine ads and billboards as part of a Gap holiday ad campaign. Plus, the service, which passed 5 million members recently, is poised to go toe-to-toe with Facebook for control of that market. But beneath the simmering fight to own the check-in, several startups with smaller user bases are carving out their own niches.