An addition to my previous post on patents is due.
If you are a non-producing entity, ie you have a patent “just to have it” (you’re a company, not a person, and you only have patents to use as legal ammunition), you relinquish rights to sue over infringement.
If you are not producing anything the patent covers, just like with a trademark, you lose it. Holding a patent to use as legal weaponry is at the least unethical, and likely worse – add-in the fact that the legal system currently makes it [relatively] simple for trolls to operate … and you have a totally messed-up system.
Wired has a great article on patent trolls in issue 20.12 (see also this article on patent drawings).