The New Yorker: The Facebook Generation: "In the May 15, 2006, issue of The New Yorker, John Cassidy reports on Facebook, an on-line social network primarily for college students, and on how its creator, Mark Zuckerberg, avoided some of the pitfalls of similar services ('Me Media,' p. 50). Facebook, Cassidy explains, like other popular sites such as Friendster and MySpace, 'invited members to post a photograph and a few personal details -- a profile --and link to other members, exploit[ing] the peculiar logic of networks, by which large numbers of people are connected through a small number of intermediaries and become part of a vast virtual community.' When Zuckerberg started the web site near the end of his sophomore year at Harvard, in 2004, he intended it to be an on-line extension of the campus, a place for fellow-students to share information. That idea of a more intimate on-line network caught on quickly, and, two years later, there are seven and a half million registered users in more than two thousand colleges around the country, making Facebook by some measures one of the most popular sites on the Web. "
Excellent article; unfortunately the full article is not available on-line, but the summary linked-to above continues for a couple more paragraphs.