Foursquare's Dennis Crowley on Building a Massive Community

If you've "checked in" to an urban hotspot, say thank you to Dennis Crowley, the 36-year-old co-founder of location-based social tool Foursquare. Using Foursquare's smartphone app, users can discover local businesses and places to go, and share their discoveries and whereabouts with friends -- often while earning badges and saving money through special offers.

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