Forbes just released its annual Forbes 400 list of the richest Americans, and billionaire Microsoft founder Bill Gates (above) is back on top after briefly ceding first place to Warren Buffett this spring. Gates has a net worth of $57 billion as opposed to Buffett's $50 billion - $12 billion less than he had several months ago before Berkshire Hathaway's stock plummeted 15%. Buffett isn't the only one to suffer a major reversal. The year's biggest loser was Sands casino mogul Sheldon Adelson, No. 15, whose fortune fell $13 billion in the past 12 months - about $1.5 million per hour, Forbes notes - to $15 billion.

Adelson's fellow casino kingpin Kirk Kerkorian, No. 27, was another underachiever, losing $6.8 billion this year. Still, they were both better off than the 33 moguls who fell off the list altogether due to declining fortunes. On the plus side, 31 new plutocrats moved up to take their places, including Facebook founder Mark Zuckerberg, 24, who makes his debut on the list with an estimated net worth of $1.5 billion.

Other Forbes 400 first-timers include fertilizer tycoon Alexander Rovt, car dealer and art collector Norman Braman, and Patrón tequila founder John Paul DeJoria. Meanwhile, New York City's billionaire mayor Michael Bloomberg was the year's biggest gainer, as his net worth jumped $8 billion to a total of $20 billion, snagging him the No. 8 position. Also worth noting among this year's stats:

The average net worth of Forbes 400 members is $3.9 billion.
There are 42 women on the list with an average net worth of $4.2 billion.
For the 2nd year in a row, the minimum net worth needed to make the list is $1.3 billion.
The assembled net worth of the richest Americans rose by only 2%, or $30 billion, to $1.57 trillion this year.

See the complete list here.

Here's a unique mark of inflation, Warren Buffett's annual auctioned lunch brought in more than three times the amount that it did last year. Last year, the lucky luncher bid $650,100 but this year, Chinese businessman Zhao Danyang offered $2.1 million to lunch with the famous investor at the Smith and Wollensky steakhouse in New York. Back in 2005, the winning bidder paid just $351,100 for the privlege.

The proceeds go to a non-profit foundation which fights poverty and homelessness.. So far Buffett has raised over $4 million but selling himself each year but his biggest charitable move has been his declaration that he will give the bulk of his fortune to the charitable foundation set up by Bill and Melinda Gates.

[Thanks, Ben]!

The winning bid for lunch with Warren Buffett this year was $620,100. The bidding was all done by five individuals and the winner, whose eBay name is "fastisslow," will be able to take 7 friends to lunch with Buffett. All the proceeds of the auction, which was the second highest charitable auction ever on eBay, will all go to the Glide Foundation, a non-profit San Francisco group that provides services and food to the homeless.

The most expensive charity auction on eBay was for a celebrity-autographed Harley that sold for over $800,000, and the next most expensive was a lunch with Tiger Woods, which sold in 2001 for $425,000.

Warren Buffett recently announced that he plans to give away the majority of his fortune upon his death. Many expected the bulk of his holdings to be given to the Susan Thompson Buffett Foundation, which was founded by Buffett's late wife, but it now appears that the largest contribution of $30.1 billion will go to the Gates Foundation. A contribution of that size would double the size of the foundation, already the world's largest. His wife's foundation will receive approximately $3 billion, while the three foundations run by each of his children will get over $1 billion each.

The billionaire is in excellent health now and has a net worth of approximately $42 billion dollars

Every year, Warren Buffett offers up the opportunity to have lunch with him in an auction that benefits the Glide Foundation. The tradition of auctioning a lunch began in 2004, when Buffett first became involved with the San Francisco nonprofit, which offers programs to help the poor, hungry and homeless. In early years, lunches often sold for $25-30,000, but when they switched the auctions onto eBay in 2003, making them much more visible, the numbers shot up dramatically. Last year's lunch with Warren sold for $351,100.

The auction will begin on June 22 and the starting price is $25,000.