There's a popular business book out right now called the Tipping Point by Malcolm Gladwell. In it he explains how big trends are started by a few people. He calls them connectors and mavens. These are the people who know everyone.
I read the book about a year ago and found myself skeptical. Some parts resonated with me, others rang hollow. For example, the author explains Paul Revere's successful ride and the failure of William Dawes (who made a similar ride with much less effect) by saying that Paul Revere was a connector while Dawes was not. Except, he never proves Revere was a connector except by way of results. Connectors are able to move the masses and we can see this because Paul Revere was a connector and moved the masses. How do we know he was a connector? Well, because he moved the masses. That's circular at best.
Fast Company examines the phenomemon described by Gladwell and finds it lacking. A very interesting read.