The latest 13F season is commencing, 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 GAMCO Investors (GBL 0.37%), the diversified asset manager and financial services company headed by well-known value investor Mario Gabelli. According to its recently released 13F statement, the company upped its position in Diebold Incorporated (DBD) by 21%, while adding new positions in Responsys (NASDAQ: MKTG) and ViroPharma Incorporated (NASDAQ: VPHM).

Diebold specializes in machinery such as ATMs, check-cashing machines, safes, and pneumatic tube systems, and also offers software. Its stock surged nearly 10% yesterday, on fourth-quarter results that featured estimate-topping revenue and earnings a bit below expectations. Revenue was down from year-ago levels, but management expects increases. Diebold stock yields 3.4%, and the company has a very long record of consecutive dividend increases, though recent increases have been getting smaller. Among hundreds of holdings, GAMCO's Diebold position was its 28th largest at the end of the quarter, valued at more than $146 million.

Responsys offers software that focuses on relationship-based marketing, among other things. Bulls see growing corporate budgets for targeted marketing, and like the fact that unlike some rivals, Responsys is actually profitable. Its client list is growing, with management noting that "In the second quarter, we signed many new North American clients, including iconic fashion brand J. Crew; jewelry and watchmaker, Swiss Watch; and next-generation event technology website, Eventbrite." Responsys recently bought Push IO, a major provider of push notifications that are delivered mainly over mobile devices now, but could spread to websites, gaming devices, and beyond. This matters, because right now push notifications have stronger open and click-through rates than emails. Meanwhile, there's murmuring that a bigger entity might want to gobble up Responsys itself. Valued at nearly $11 million, GAMCO's position in Responsys is far from its largest.

ViroPharma and its key product Cinryze, which treats the rare condition of hereditary angioedema, have been acquired by Shire plc (NASDAQ: SHPG). With a $29 billion market cap and a 0.10% dividend, Shire is aiming to deliver growth more than income. Shire expects Cinryze sales to account for 40% of its revenue. But overall, the acquisition reflects how attractive orphan drugs can be, and it's fueling speculation about other possible buyouts. Shire's fourth-quarter was strong, but the company did experience a setback with poor clinical trial results for its major depressive disorder drug Vyvance. With more than $33.6 million worth of shares, ViroPharma was GAMCO's 155th-largest holding in the quarter.