Published: Feb 26, 2011 11:51 PM EST
Updated: Feb 26, 2011 8:51 PM EST

OMAHA, Neb. (AP) - Billionaire Warren Buffett wants Americans to be optimistic about the country's future but wary about borrowing money and the games public companies play with profit numbers they report.

Buffett said in his annual letter to Berkshire Hathaway shareholders Saturday that he still believes America's best days are ahead.

"Commentators today often talk of 'great uncertainty.' But think back, for example, to December 6, 1941, October 18, 1987 and September 10, 2001," Buffett wrote, referring to the days before the Pearl Harbor attack, a stock market crash and terrorist attacks in the U.S. "No matter how serene today may be, tomorrow is always uncertain. Don't let that reality spook you."

He said a housing recovery will likely begin within the next year, which would help the economy and several Berkshire subsidiaries, including ones that make carpets and bricks.

Buffett's letter detailed how the acquisition of Burlington Northern Santa Fe railroad, better results at Berkshire's other subsidiaries and a $1.9 billion paper gain on investments and derivatives combined to boost the company's net income by 61 percent to $12.97 billion on revenue of $136.2 billion in 2010.

The letter was full of good news for Berkshire investors because nearly all of its businesses, except the ones linked to housing, performed well, said Glenn Tongue, a managing partner at T2Partners investment firm.

"I think his tone in this letter was more optimistic than usual - both about the economy and the business," Tongue said.

Buffett also devoted part of his message to educating investors on key business principles. Buffett said the financial crisis of 2008 confirmed the dangers of investing with borrowed money because even a short absence of credit can ruin a company.

"When leverage works, it magnifies your gains. Your spouse thinks you're clever, and your neighbors get envious. But leverage is addictive," Buffett said. "Once having profited from its wonders, very few people retreat to more conservative practices."

That's part of why Berkshire always keeps at least $20 billion cash on hand for unforeseen events or investment opportunities, he said. At the end of 2010, its cash reserve totaled $38 billion.

Buffett urged investors not to focus on the net income figures that companies report because they are easily manipulated through accounting tricks or by selling investments. He said Berkshire's net income can be particularly misleading because of the large amount of unrealized investment gains or losses the company holds at any given time.

He said that regardless of Berkshire's performance, it could easily and legally "cause net income in any given period to be almost any number we would like."

Buffett also offered Berkshire shareholders few new details about how the company would function once he is no longer running it.

The 80-year-old chairman and CEO of Berkshire said that investment manager Todd Combs will manage $1 billion to $3 billion of Berkshire's $158 billion investment portfolio. Berkshire hired Combs last fall, and Buffett says Combs has the risk aversion, dedication and track record he wants in an investment manager.

To replace Buffett, Berkshire plans to split his job into three parts - chief executive officer, chairman and several investment managers. Buffett, however, has indicated that he has no plans to retire, and he says he loves his work and remains in good health.

Many people speculate that David Sokol, who is chairman of NetJets and MidAmerican Energy, is the leading candidate to be Berkshire's next CEO. But several other Berkshire managers have been mentioned as possible chief executives, including: Ajit Jain, who runs Berkshire's reinsurance division; Tony Nicely, chief executive of Berkshire subsidiary Geico; and BNSF CEO Matt Rose.

Buffett praised all those managers in his letter Saturday.

Buffett has said previously that the company has three outstanding internal candidates for CEO, but he has refused to name them.

Buffett also reminded investors that Berkshire has little chance of matching its past stellar performance because the company is so large. Buffett's