The latest 13F season is here, when many money managers issue required reports on their holdings. It can be worthwhile to pay attention, as you might get an investment idea or two by seeing what some major investors have been buying and selling.

For example, consider highly regarded value investor David Einhorn, founder of Greenlight Capital. Einhorn's investing success, along with 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 in which he feels a stock is mispriced. He started Greenlight with less than a million dollars, and it now boasts a stock portfolio worth $6.7 billion.

Greenlight Capital's latest 13F report shows that it sold off some or all of its positions in Delphi Automotive PLC (NYSE:DLPH), Micron Technology, (NASDAQ:MU), and NCR Corporation (NYSE:NCR).

Delphi Automotive's stock has gained more than 40% over the past year, recently hitting an all-time high. The company makes vehicle components and has been boosted by the recovering auto market. Indeed, it expects to double its revenue in China to nearly $5.5 billion thanks to the growing vehicle market there. Delphi is not clinging to traditional technology, either, as it recently signed an agreement with Westport Innovations to jointly develop high pressure direct natural gas injectors. (Westport specializes in natural-gas engines and fuel systems.) Meanwhile, Delphi is busy cranking out replacement parts for General Motors as the carmaker addresses the recall of 2.6 million vehicles with flawed ignition switches. (Both companies are also being sued over the switches.) Delphi's first quarter featured revenue up 6% year over year and earnings per share rising 18% and topping estimates as management upped its guidance for the year. Delphi's stock yields 1.4%.

Micron Technology's stock has surged some 140% over the past year, and its forward P/E ratio is still just near 11, suggesting that it's attractively priced. The company's second quarter featured expenses falling and revenue roughly doubling. Bulls see demand growing for solid state drives and 3D NAND technology, too, which can drive growth. Stabilizing DRAM and NAND prices are also a plus. My colleague Anders Bylund has dubbed Micron "a high-octane growth stock, but priced like a sleepy value play." Some expect the company to start paying a dividend again one of these days, too, as its free cash flow is substantial and profit margins are growing. A bit of unwelcome news recently was the company's fall  from second-largest to third-largest DRAM chip maker, though it remains in second place in global DRAM revenue.

NCR Corporation, which was once National Cash Register, is now in the business of hardware, software, and services related to ATMs, point-of-sale retail terminals, self-serve kiosks, and more. It's poised to benefit from retailers and banks upgrading their equipment to deal with the new, more secure, EMV standard, which calls for chip-embedded credit and bank cards. The company is also moving into the mobile realm, with tools such as its NCR Mobile Pay app. NCR's last quarter featured revenue rising 8% year over year and earnings topping estimates, though the company also lowered projections for 2014.