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.