Starbucks was an early adapter of this strategy, offering a "barista" badge to those with more than five check-ins at different locations. Starbucks then offered the "mayors" off each location a free Frappuccino. RadioShack did something similar, though less creative, and offered new customers a 10 percent discount if they check into a store using the service.

2. Google Maps

We normally think of Web mapping services as a staple necessity to get from point A to point B. But when in real time, it further blurred the distinction between a map service and a social location service. The feature works for Android devices and syncs with Latitude, Google's Foursquare duplicate. Each time a user checks in via Google Maps, they're given options to share their location with their friends on Latitude or to post it publicly.

Business Upside: While Latitude doesn't offer notable improvements over Foursquare, having check-ins available to the wider public via Google Maps -- and its 200 million users -- is a potential way to reach would-be customers who don't use social networks at all, and are simply utilizing the map service for directions.

3. Facebook Places