America's super high net worth individuals saw their net worth grow by 13 percent in the past year to $1.7 trillion, according to Forbes annual wealth survey. Collectively, their wealth and assets are equivalent to Bhutan's 2011 gross domestic product.

At the same time, the average net worth of the 400 wealthiest Americans rose to a record $4.2 billion, up more than 10 percent from a year ago, while the lowest net worth came in at $1.1 billion versus $1.05 billion last year, said Forbes.

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Not surprisingly, Bill Gates (Microsoft), Warren Buffett (Berkshire Hathaway) and Larry Ellison (Oracle) held on to their top spots at number 1, 2, and 3 with their wealth estimated $66 billion, $46 billion and $41 billion respectively.

It was, however, a bad year for social media moguls, whose net worth fell by a combined $11 billion.

Mark Zuckerberg, founder and CEO of the largest social networking site Facebook, came in at number 36 as the biggest loser of the year: his net worth fell dramatically by $8.1 billion to $9.4 billion.

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Dismal performances by other social media stocks dropped some executives from Forbes' rich list altogether, including Groupon's Eric Lefkofsky, number 293 on last year's list, and Zynga's Mark Pincus, number 212 on the 2011 list.

Collectively, the total wealth of 400 of America's richest is equivalent to one-eighth of the entire US economy, which stood at $13.56 trillion in real terms according to the latest government data.

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Forbes commented on the findings:

There has been much discussion of late about the widening gap between rich and poor and what role the wealthiest Americans should play in fixing society's ills, and how much taxes they should pay. This list on the surface will perhaps exacerbate these concerns, but a deeper analysis instills confidence that the American dream is still very much alive. Seventy percent of the Forbes 400 members made their fortunes entirely from scratch; of the 20 newcomers who climbed into the ranks, only four inherited.

Coincidentally, the Wall Street Journal reported yesterday that "Bill Gates and Warren Buffett have persuaded 11 more of their billionaire peers to promise to give away half of their wealth" as part of the Giving Pledge.

In an interview with the Journal, Gates said "the goal [of the Giving Pledge] is to raise the visibility of philanthropy and the great things it can do."

The two-year old programme currently has 92 families pledging to give away a majority of their fortunes. Gates and Buffett are the most generous Americans on the Forbes list, having given away $28 billion and $17.5 billion to date, respectively.

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