Ars Technica:

…Three Boston University researchers have produced a rigorous empirical estimate of the cost of patent trolling. And the number is breath-taking: patent trolls (“non-practicing entity” is the clinical term) have cost publicly traded defendants $500 billion since 1990. And the problem has become most severe in recent years. In the last four years, the costs have averaged $83 billion per year. The study says this is more than a quarter of US industrial research and development spending during those years.

In this economy, I suppose we should take heart that patent lawyers are getting rich, at least.