The case of private Bradley Manning passing on thousands of documents to WikiLeaks raises important questions that have no clear answers. Depending on where you stand, his behavior lies somewhere between breaching national security and fostering the right to know of the public. He did plead guilty and might stand to receive a life prison sentence, but this raises the issue that these extreme sentences might discourage future whistle-blowers.
A very interesting article on the subject in The New York Times by Floyd Abrams and Yochai Benkler entitled "Death to Whistle-Blowers" shows both sides of the argument and is well worth reading.