Some of the biggest news in Forbes' list of 400 richest Americans is the growing wealth of 26-year-old Facebook CEO Mark Zuckerberg. Zuckerberg's net worth is currently estimated to be $6.9 billion; he is planning to donate $100 million to the Newark, New Jersey public school system. Cynics point out that Zuckerberg's generous philanthropy could be a crafted PR move scheduled a week before "The Social Network," a not-entirely-complimentary movie about Zuckerberg comes out. All the same, we wanted to know: how do billionaires spend their money? For the answer, we spoke with Robert Frank, the Wall Street Journal's Private Wealth Reporter and author of "Richistan: A Journey Through the American Wealth Boom and the Lives of the New Rich."

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