You may not be familiar with David Einhorn, but he's a highly regarded value investor who runs the prominent Greenlight Capital hedge fund. He started Greenlight with less than $1 million, and it now boasts a stock portfolio worth more than $5 billion. Greenlight Capital has averaged close to a 20% annual return since its 1996 inception.

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 he looks for situations where he feels a stock is mispriced. He also isn't afraid to speak his mind when heavily invested in various companies. He even sued Apple, which was recently his largest holding, when he didn't like what it was doing -- though he later dropped the suit.

Greenlight's latest quarterly 13F filing shows us some interesting moves that Einhorn and his team have made recently and reveals some of their thinking.

Buys and sells
First off, Greenlight Capital boosted its position in Spirit AeroSystems (NYSE:SPR) by 41% in its third quarter. Spirit Aerosystem, a subsidiary of Onex that makes aviation equipment, has seen its stock more than double over the past year. It focuses on fuselage systems, propulsion systems, and wing systems, and it has been buoyed by Boeing's recent sales. Spirit AeroSystems also got a boost from its third-quarter earnings report, which topped expectations and featured a 10% rise in revenue and a return to profitability. Also making many happy is its record order backlog of $38 billion.

Greenlight Capital reduced its position in Rite Aid (NYSE:RAD) by 20% and in Computer Sciences (NYSE:CSC) by 13%. Drugstore chain Rite Aid has had a very tough run lately, but it has been getting its act together and its stock has surged fivefold over the past year. Bears worry, though, about its debt and that its revenue isn't growing briskly. They see its rivals sporting stronger numbers -- and paying dividends, too. Bulls believe that if Rite Aid can keep growing, it can keep rewarding shareholders. Still, its stock isn't exactly cheap at recent levels.

Information technology outsourcing and service provider CSC has risen close to 50% over the past year, but not without bumps along the way. The company has been shifting its focus from infrastructure sales to more profitable software and services, and it has bought companies such as big-data specialist Infochimps and cloud services start-up ServiceMesh. But it has also been dealing with a multiyear investigation by the Securities and Exchange Commission into its accounting. In its last quarter, Computer Sciences posted estimate-topping earnings, up 35% over year-ago levels, but revenue sank by 10%, underperforming estimates. The company is not firing on all cylinders at the moment, but patient believers are receiving a 1.5% dividend yield and benefiting from share buybacks.

No one should just blindly mimic the moves of any impressive investor, but it can be useful to keep an eye on them. The stocks they buy, sell, or hold can present us with useful ideas.

Longtime Fool contributor Selena Maranjianwhom you can follow on Twitter, owns shares of Apple. The Motley Fool recommends Spirit AeroSystems Holdings. It recommends and owns shares of Apple. Try any of our Foolish newsletter services free for 30 days. We Fools may not 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.