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 Citadel Advisors, founded and run by Kenneth Griffin. It's one of the biggest hedge fund companies around, with a reportable stock portfolio totaling $72.5 billion in value as of March 31, 2014. According to the folks at, Griffin and his team use "a combination of advanced computer code, complicated financial algorithms and secrecy. Griffin was using quantitative, technology-based methods before many other firms had cell phones."

Citadel Advisors' latest 13F report shows that it shrank its positions in EMC Corporation (NYSE:EMC), Micron Technology (NASDAQ:MU), and Kodiak Oil & Gas Corp (UNKNOWN:KOG.DL).

EMC Corporation is a storage giant, positioned to profit from the rapidly growing cloud-computing and "big data" arenas. It holds an 80% ownership stake in virtualization specialist VMware, too, and has made some significant acquisitions recently, such as storage software developer ScaleIO and flash equipment maker DSSD. With EMC's forward price-to-earnings (P/E) ratio near 12, it seems attractively priced. It hasn't been growing briskly, but its top line has been steadily increasing. It also has many initiatives that could pay off well in the future, such as its RSA Security business and Pivotal, which has been likened to "an OS for the cloud." EMC initiated a dividend last year and yields 1.7%. Bulls like its sizable share repurchases, too.

Micron Technology posted second quarter results featuring falling costs and revenue roughly doubling. With demand growing for solid state drives (SSDs), bulls like the company's investments in NAND memory technology, and see demand for 3D NAND technology driving growth at Micron and elsewhere. The company's forward P/E ratio is near 10, and my colleague Anders Bylund has dubbed Micron "a high-octane growth stock, but priced like a sleepy value play." Analysts at RBC Capital agree, recently upgrading the stock to outperform, citing improving NAND quality and rising margins. Micron Technology hasn't paid a dividend since the 1990s, but with hefty free cash flow and growing profit margins, many would like to see a dividend reappear. Even without that, though, the company is rewarding shareholders via aggressive stock buybacks. Its stock has more than doubled over each of the past two years and is near a 52-week high.

Kodiak Oil & Gas recently posted disappointing first-quarter results, in part due to a combination of harsh winter conditions and the kind of wells Kodiak was drilling in North Dakota. The company is a top operator in the promising Bakken Shale region and has been boosting production while cutting costs. One way it's aiming to boost production is by drilling wells closer together, an approach called "downspacing." Bears worry about Kodiak's significant debt load, but much of the funds borrowed have been used to invest in future growth.