Led by MySpace, social networking is a cultural phenomenon that is still developing a stable revenue model. Even so, it is estimated that in 2007 marketers will spend $900 million on advertising and marketing on social network sites in the US, mostly to create profile pages and sponsored promotions. Online social networking have become a cultural phenomenon over the past several year, sparking thousands of media stories, blog postings and television exposes. The basic concept is simple enough: Online social networks enable people to create profiles, describe their interests, share their thoughts in blogs or postings, and connect with other people. But the variations on the theme are endless. MySpace, still the largest player by far, is estimated to generate $525 million in the US this year. Facebook is expected to generate $125 million and both should continue to see healthy revenue increases. Combined, the two account for 72% of US social network ad spending in 2007 and 75% in 2008.