I stumbled across this article describing how an inventor got screwed out of money by Lucent because Lucent used the inventor's invention to do something for an unnamed US agency: http://www.wired.com/news/technology/0,68894-0.html (http://www.wired.com/news/technology/0,68894-0.html).
While I realize that this article may just be trying to scare us about the Big Bad US Government, it did point out to me something I did not know before - the US government has a "privilege" never awarded to it lawfully that lets it intervene in civil matters. Oh, and of course George Dubya's government has used it the most of all the US governments to ever have used it.
Not getting paid for an invention because I'm not allowed to sue the person I sold the invention to because of state security secrecy privilege really sucks, though.
As noted on the third page of the article, the same statute was used to quash Maher Arar (http://www.cbc.ca/news/background/arar/) law suit against the US government over his being seized by the Americans and sent to Syria to be tortured for a year. As Thorin noted, this is a big stick being used more and more by the American government.
search on Google for "eminent domain" and "New London" -- the principle is likely the same.
Heck, in the movie "Contact", James Woods' evil NSA character said something like "if this isn't a case for eminent domain, I don't know what is..." i.e. if the gubmint can find a use for your invention, and they don't need you anymore, well, buh-bye!
Not a top-secret agency or anything - just more examples of the US government abusing power, eminent domain, etc.
http://www.nissan.com/Digest/The_Story.php