It's official: Facebook is soundly thrashing one-time social network leader MySpace, though the site credited with kick-starting the mainstream social networking gold rush was far and away the No. 2 social site. Tagged was No. 3 at 2.4 percent of the September 2009 U.S. share, with Twitter and MyYearbook rounding out the top five social site ranks, grabbing 1.8 percent and 1 percent share, respectively.

Twitter boasted astronomical growth, up 1,170 percent from its negligible 0.15 percent market share from September 2008. As far as social sites go, Twitter is positioned to be Facebook's biggest challenger.

While the site's functionality is limited to 140-character messages and real-time search, the microblogging service is armed with an undisclosed new round of financing and is in the midst of rolling out its geolocation API and a lists feature to help members curate groups online. However, Facebook has shown an inclination toward moving closer to real-time search, and both sites seem to be swapping features.

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