Facebook is just a baby, only two years old. It is also the second largest social network on the web, with over 8 million members. Over the years it has expanded to include university, high school and company networks. Members can now upload an unlimited number of pictures. The most recent expansion is a news-feed that tracks what you and your friends are doing while on the Facebook site (posting comments, pictures, updating profile, etc).
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History of Facebook
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Marketplace Report: A Billion-Dollar Facebook Deal
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Facebook.com Expands Amid Rumors of Buyout