Warren Buffett tops the list of the biggest losers among America's richest billionaires, with an estimated $10 billion drop in his personal wealth over the past twelve months. That's the result of Berkshire Hathaway's 20 percent stock decline.

But Buffett's remaining $40 billion is still enough to maintain his number two ranking on the just-released annual Forbes 400 ranking of the country's wealthiest people.

Microsoft founder Bill Gates, Buffett's friend and bridge partner, also kept his #1 position, with an estimated $50 billion. That's down $7 billion from last year.

They're not alone. Forbes says the collective net worth of the nation's 400 richest fell from $1.57 trillion to $1.27 trillion over the year. It's only the fifth time that's happened.