At last night's excellent event at Luciano's, Bob Barr addressed (among other things) how the United States intercepts and reviews emails based on whether the interceptor reasonably believes one party to the communication is outside of the country. For this and other reasons, many do not trust the privacy and security of email and electronic communications, because the United States government intercepts, stores, and reviews those communications.
The principal reason the Unites States government has this ability is because most Internet traffic in the world is routed through the United States. An article in tomorrow's (Aug. 30, 2008) New York Times addresses the current free-market response to the U.S.'s invasion of privacy: more Internet traffic is now being routed outside of the United States, and businesses and companies are aggressively building Internet infrastructure outside of the United States. While certainly some amount of development outside of the U.S. is inevitable, I have no doubt that the U.S. has lost some amount of commerce because its government does not respect the privacy of communications through the Internet.
And, it also increases the ability of true enemies of the United States to hide their Internet communications from legitimate surveillance techniques (e.g., those performed pursuant to a warrant issued by a judge that is based upon a showing of probable cause).