Facebook has not only helped people to make zillions of new connections, it has also inspired a screenplay. A film called “The Social Network”, due to be released later this year, will trace the site’s meteoric rise from its foundation in 2004 to become king of the social-networking world. How have social networks managed to shoot to such prominence that they are already being given the Hollywood treatment?The most important reason for their phenomenal growth is something called the “network effect”. Originally coined to describe the rapid spread of telephones, this states that the value of a communications network to its users rises exponentially with the number of people connected to it. This implies that the audience of a social network will grow slowly at first, then explode once it passes a certain point. Jeff Weiner, the chief executive of LinkedIn, which now has some 58m members, says it took the company 16 months to reach its first million users, whereas the most recent additional million came on board in only 11 days. Facebook has had a similar experience. It took almost five years to drum up its first 150m users, but just eight months to double that number.
http://www.economist.com/specialreports/displaystory.cfm?story_id=15350972