Buffett is worried about health care costs, not banks.

FORTUNE -- At Berkshire Hathaway's (BRKA) annual meeting on Saturday, Warren Buffett fielded questions from investors, journalists, analysts and, for the first time, invited onto the stage one investor, Doug Kass, who is betting against Berkshire's stocks. ("You haven't convinced us yet to sell our stock, but keep working," said Buffett in response to one question.) The questions ranged from those about the challenges facing America, the Fed's stimulus efforts and underwear (Berkshire owns Fruit of the Loom). Here's what we learned:

1) The biggest threat facing the U.S. economy is rising health care costs, says Buffett. The U.S. economy spends 17.5 cents of every dollar on health care, compared to 8 cents in other countries. Buffett said that's a major competitive disadvantage.

2) Corporate profits may have peaked, at least as a percentage of the economy. Buffett says corporations have made an amazing recovery, but he notes that the unemployment rate remains high. He said he thought that dichotomy would remain a topic of "public discourse." But he thinks GDP will grow. So not all bad.

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3) Buffett hasn't been to Mt. Gox. He says doesn't know much about Bitcoin, the virtual currency that has been gotten a lot of buzz lately. Buffett's partner Charlie Munger said that he has no confidence that Bitcoin will become a viable meaningful currency. Buffett said he thinks the dollar will remain the world's default currency for years to come, perhaps forever. "Of our $49 billion, we haven't moved any of it into Bitcoins," says Buffett.

4) Buffett isn't worried about another financial crisis, but Munger may be. Buffett says he doesn't worry about banks creating the next bubble or bust. And he says he has no plans to sell the shares he has in any of the big banks, including Wells Fargo (WFC), U.S. Bancorp (USB), and M&T Bancorp (MTB). But Buffett does say that Dodd-Frank and other new regulations have lowered the returns banks can generate.

Munger, though, says he thinks more should be done to rein in the big banks. For one, he thinks the market for financial derivatives has gotten too big and should be separated from traditional banks. "The financial statements of big banks are hard to understand," says Munger.

5) Buffett still has to defend his investment in newspapers. For the first time, Buffett says he's getting a tax benefit from buying small newspapers.

6) Buffett is still bullish on America. "I believe a baby born in America today will have better opportunities in life than ever before," says Buffett.