A prominent computer security expert was barred from boarding one United flight, removed from another, and detained by the FBI all apparently over a tweet pointing out how easy Uniteds security system would be to hack.
http://gawker.com/security-expert-removed-from-flight-and-detained-by-fbi-1698844214
http://gawker.com/security-expert-removed-from-flight-and-detained-by-fbi-1698844214