According to a research paper from Boston University, patent trolls costs U.S. companies and other organizations a staggering $29 billion last year. The study analyzed the effect of intellectual property rights claims made by organizations that own and license patents without producing related goods of their own. Some would say that this is the very definition of a patent troll: a company that buys or licenses patents with the express purpose of litigating its way to financial success.
The research covered companies that called themselves "non-practicing entities" (NPEs), which includes businesses that buy patents to license them out, individual inventors, universities, and companies that assert patent rights unrelated to the products they make.
The study found that the direct costs included legal and license fees. The study's authors, James Bessen and Michael Meurer from Boston University's school of law, said that there are other charges that the study didn't document. This means that their study only reflected part of the serious impact patent trolling has.
"This [$29bn] figure does not include indirect costs to the defendants' businesses such as diversion of resources, delays in new products, and loss of market share," the authors wrote. "Even so, the direct costs are large relative to total spending on [research and development], which totaled $247bn in 2009, implying that NPE patent assertations effectively impose a significant tax on investment in innovation."
You can read more on this topic in this BBC article.