Mass Interpersonal Persuasion
"Facebook is the precursor of something I'm calling mass interpersonal persuasion. That is a new phenomenon and the most important thing to happen in the world of persuasion since the advent of the radio over 100 years ago. Radio changed the game for persuasion because it allowed a message to be broadcast to thousands and millions of people, which was previously not possible. TV was an extension of that, but I don't think it was the big leap that radio was.
Facebook takes very strong interpersonal influence dynamics -- the way people persuade each other face-to-face in small groups with peer pressure, reciprocity, flattery -- and allows those to be used on a mass scale because your social networks are built in. Friends influence friends, who influence friends, and that keeps rippling out. They can reach people very quickly for very little cost and ordinary people can set these in motion. It doesn't require a big broadcasting company or a big PR campaign. If you get the right message in the right way, you'll effect millions of people. Facebook has been the best platform for that, but I think in the future it will be commonplace." (http://www.fastcompany.com/articles/2008/05/interview-bjfogg-on-facebook.html)