EVEN GREAT INVESTORS MAKE MISTAKES. Warren Buffett's affinity for a group of financial stocks, including American Express (AXP), Wells Fargo (WFC) and U.S. Bancorp (USB), is likely hurting his equity returns in 2009.

vaunted equity portfolio, which totaled $76 billion at the end of the third quarter, the latest reporting period.

We estimate Berkshire's equity portfolio could have dropped 14% in 2009 through Thursday, against an 8% decline in the S&P 500.

Our estimate is based on the change in value of Berkshire's 16 largest equity holdings. These holdings historically have accounted for over 85% of Berkshire's portfolio. The tough 2009 follows a good showing in 2008, when Berkshire's equity positions declined -- by our estimate -- about 25%, 13 percentage points better than the S&P 500. Our calculations for 2009 are based on Berkshire's reported holdings on Sept. 30. There admittedly may have been some changes since.

Berkshire owns a stake in Buffalo's M&T Bank (MTB)

Our guess is that if any of these companies needs an equity investor, Berkshire stands ready to help. And the stocks are so volatile they could turn higher at any time.

The paper losses on Berkshire's equity portfolio this year, plus losses on its short position in some $37 billion of equity puts, have depressed Berkshire class A shares, which finished Friday at $86,250, down 10% in 2009. Barron's wrote bearishly on Berkshire in late 2007 when the stock traded at $144,000 and we turned bullish in late November with the shares just above current levels.

When it reported third-quarter results in November, Berkshire said shareholder equity fell by $9 billion, or nearly $6,000 a share, through the end of October given weak markets. We estimate book value probably ended 2008 around $70,000 a share. Current book value may have dropped close to $67,000 a share. If we're right, Berkshire trades for a still-reasonable 1.3 times book value and 14 times projected 2009 earnings of around $6,000 a share.

After a flurry of high-profile investments in early October, including $5 billion in Goldman Sachs preferred carrying a 10% dividend, and a similar $3 billion deal involving General Electric , Berkshire hasn't unveiled any big new investments. Why? Our guess is that its once-enormous cash hoard has been depleted.

Berkshire's insurance cash holdings, which stood at $27 billion on Sept. 30, likely fell to $13 billion after the Goldman (GS) and GE (GE) deals, as well as a $6.5 billion investment in junk bonds and preferred stock of Wrigley, which was bought by Mars. Berkshire also is on the hook for a $3 billion convertible preferred-stock investment in Dow Chemical (DOW) if it completes its purchase of Rohm & Haas (ROH) . Some investors say Berkshire likes to keep $10 billion of cash to deal with unexpected insurance claims arising from an earthquake or hurricane. This wouldn't leave Berkshire much cash for a big investment unless it sells something or takes on debt.

Our guess is that if Berkshire did make more fourth-quarter investments, they were focused on the battered junk-bond market. Berkshire will disclose more on investments in its annual report, due around March 1.

The Bottom Line
Berkshire's class A shares are down 10% in 2009 to $86,250, a reasonable level that we estimate at 1.3 times book and 14 times projected 2009 earnings of $6,000 a share. That looks appealing.