At The Motley Fool, we understand that it often pays to zig when Wall Street zags, but that doesn't mean that we don't pay attention to what leading fund managers are buying and selling. And funds that aren't always in lockstep with the broader market can be a particularly valuable source of insight.

Every quarter, fund managers overseeing more than $100 million must disclose their quarter-end holdings publicly by filing Securities and Exchange Commission Form 13-F. The form lists all U.S.-traded securities the manager held at the end of the quarter. Although the form doesn't disclose the manager's short positions or the manager's intraquarter trades, it can shine a bright light on his or her "long" stock bets.

Q3 2011 update
Value investor David Einhorn founded Greenlight Capital and his investing success, as well as his advocacy of financial transparency and accountability, have attracted many fans. Although Einhorn isn't afraid to short stocks, he prefers going long, and looks for situations where he feels a stock is mispriced.

Why should you look at Greenlight Capital's moves? Well, according to the folks at GuruFocus.com, between 2006 and 2010, Greenlight gained 66%, compared with just 12% for the S&P 500.

The total market value of Greenlight Capital's disclosed equity holdings as of Sept. 30, 2011 -- the latest quarter for which data is available -- was $4.67 billion. The company's 10 largest positions and associated changes in number of shares held as of Sept. 30, 2011 were:

Apple (Nasdaq: AAPL) -- increased 21.9%.
Market Vectors Gold Miners ETF (NYSE: GDX) -- increased 104.8%.
Microsoft (Nasdaq: MSFT) -- increased 2.4%.
CareFusion (NYSE: CFN) -- increased 34.4%.
General Motors (NYSE: GM) -- increased 330.8%.
Marvell Technology (Nasdaq: MRVL) -- new.
Sprint Nextel (NYSE: S) -- increased 32%.
Travelers (NYSE: TRV) -- increased 2.9%.
Ensco (NYSE: ESV) -- increased 9.5%.
NCR (NYSE: NCR) -- increased 4.8%.

During the quarter, Greenlight also increased its position in HCA Holdings, among others. Among the stocks that it reduced its exposure to were Becton Dickinson and Employers Holdings. Also, Greenlight sold out of several stocks entirely, including Pfizer (NYSE: PFE) and BP (NYSE: BP).

Some are dismissing Pfizer because of various issues such as the patent protection expiration of its blockbuster drug Lipitor. But the company has a deal in the works with Watson Pharmaceuticals to sell a generic version of it. Also, Pfizer still has some potential big winners up its sleeve, such as a potential competitor to the blood thinner warfarin. BP has plenty of attractions for investors, such as the rising price of oil, but it's also turning some off with its connection to the big Gulf oil spill and the price it will have to pay for that.

Selected Q3 2011 commentary
Greenlight Capital has about a third of its assets in technology, far more than any other sector. Its technology stake has been growing sharply over the past few quarters, as well, while financials and health care have fallen noticeably.

Here's where the firm has been winning and losing and making new bets:

Recent winner
Apple was a big winner in the third quarter, rising about 14% when the S&P 500 sank by 14%. It has made a lot of patient investors very rich, and offers plenty of future growth potential, as its iPad invades the health-care sector, its iPod aims to displace cash registers, and as it continues to innovate with new products and applications. (Some doubt its future, though.) The company has a three-star (out of five stars) rating at Motley Fool CAPS.

Recent loser
General Motors didn't do so well, dropping more than 33% in the quarter. It's facing more trouble lately, due to concerns over crash-test-induced fires in its Chevy Volt. But many remain optimistic about the company, as it's reorganizing and streamlining itself, its management seems able, and its future looks bright not only at home but also in regions such as China. The company has a two-star rating in Motley Fool CAPS.

New bets
Greenlight Capital's largest new addition was Marvell Technology, a chip maker whose technology can make LED lights cost less. Also intriguing investors is the company's potential to serve China's hundreds of millions of smartphone users. Marvell has a four-star rating at Motley Fool CAPS.

We should never blindly copy any investor's moves, no matter how talented the investor. But it can be useful to keep an eye on what smart folks are doing. 13-F forms can be great places to find intriguing candidates for our portfolios.

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