Every quarter, many money managers have to disclose what they've bought and sold, via "13-F" filings. Their latest moves can shine a bright light on smart stock picks.

Today let's look at highly regarded value investor David Einhorn and Greenlight Capital, which he founded. Einhorn's investing success, as well as his advocacy of financial transparency and accountability, has attracted many fans. Although he isn't afraid to short stocks, he prefers going long and looks for situations where he feels a stock is mispriced.

The company's reportable stock portfolio totaled $6.0 billion in value as of Sept. 30, 2012.

Interesting developments
So what does Greenlight's latest quarterly 13-F filing tell us? Here are a few interesting details.

The biggest new holding is Yahoo! (NASDAQ:YHOO). The company recently posted encouraging quarterly results, but its new CEO, Marissa Mayer, still has her work cut out for her. There have been rumors lately that the company might partner with Facebook (NASDAQ:FB), perhaps to provide search capability, but that's in dispute -- and Yahoo! is already in a search partnership with Microsoft (NASDAQ:MSFT). Meanwhile, Mayer is reportedly reviewing  the bottom 20% of Yahoo!'s workforce, with downsizing a possibility.

Among holdings in which Greenlight increased its stake were Cigna (NYSE:CI), General Motors (NYSE:GM), Computer Sciences (NYSE:CSC), and Marvell Technology (NASDAQ:MRVL). Chipmaker Marvell took a 15% hit on reporting disappointing second-quarter earnings, and third-quarter earnings featured revenue and earnings sharply down, with the company citing weak PC demand. Some are hopeful about Marvell's partnership with LED specialist Cree (NASDAQ:CREE) to produce a dimmable LED bulb, but others would like to see it profit more from the spread of smartphones.

Greenlight reduced its stake in companies such as Apple (NASDAQ:AAPL), Seagate Technology (NASDAQ:STX), and Sprint Nextel (NYSE:S). Seagate is poised to profit from increasing storage demand from both consumers with PCs and the servers of cloud-computing companies. Input prices can be volatile, though, and it does face competition. Still, it also offers a dividend yield near 4.7%, which it has aggressively increased lately. While some see value in it, others are cautiously watching.

(NYSE:S)

Finally, Greenlight's closed positions include UnitedHealth Group (NYSE:UNH), CareFusion (NYSE:CFN), and Hess (NYSE:HES). Some see energy giant Hess as undervalued. It has been disappointing analysts in several recent quarters with its earnings, but it does hold a lot of potential, particularly in natural gas. Our analysts see a likely spinoff of Hess' refinery and downstream businesses and see recent asset sales and a restructured budget helping it dig out from a lot of debt.

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, and 13-F forms can be great places to find intriguing candidates for our portfolios.

Longtime Fool contributor Selena Maranjian, whom you can follow on Twitter,owns shares of Apple and Microsoft. The Motley Fool owns shares of Apple, Facebook, and Microsoft and has options on Facebook. Motley Fool newsletter services recommend Apple, Facebook, General Motors, Microsoft, UnitedHealth Group, and Yahoo! Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.