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Both MySpace and Facebook lost five percent of their traffic from December to January. Nielsen Online says Facebook lost 400,000 U.K. site visitors after 17 straight months of growth. "Most of the leading social networks are less popular in the U.K. than they were a year ago. It was inevitable that early growth rates couldn't be sustained and the larger networks have been plateauing over the last few months." (Photo by AP/Paul Sakuma)