They came expecting a civilized, one-on-one discussion, but they got what some attendees described as "a train wreck." Ballroom A of the Austin Convention Center was packed to capacity Sunday evening for an hour-long interview with Facebook CEO Mark Zuckerberg, the keynote speaker at this year’s South by Southwest Interactive festival. The 23-year-old billionaire founder of the social networking site was interviewed on stage by author and journalist Sarah Lacy.

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