'Flocking' behavior lands on social networking sites - USATODAY.com

John Tropea - Delicious Social Network

For example, when a friend starts exercising more, "I change my mind about how much I should be exercising or I share stories with my other friends who are influenced to do the same. You either change your behavior or you transmit information about the behavior to others, who change their behavior," says Fowler, 39. We can measure things we couldnt measure before, and that changes our perception."