I suspect you've all read about Apple and Samsung suing each other over patents.
Google's part of the story as well (it bought part of Motorola to acquire that company's patents), and Blackberry (then called Research in Motion) paid something like $500 million for patent infringement.
The Blackberry litigation, in particular, was brought by a patent "troll", a company that acquired title to a patent for something it didn't invent.
Is there a legitimate role for such entities?