"...find friends within a 10-block area..."
"When Dodgeball users 'check in' at a given locale by sending out a text message, it goes to all their preselected friends, as well as any friends of friends within a ten-block radius. A photo is sent along with the alert-which helps with identifying near strangers. Introductions are made, beer is poured, and then hookups can occur-casually, and in a low-pressure environment, all under the guise of knowing someone in common. It's Friendster, except in real time and in the real world."
Sounds fun. Also comes in handy if the government needs to locate you and ten of your friends - quickly.