From:
http://www.smartcomputing.com/editor...9g04/19g04.asp
Defamation & You.
Defamation is nothing new in the law; the concept has been around in various forms for centuries. Defamation includes both libel, which involves the publishing of false words, and slander, which applies to speech.
Although the exact components of defamation vary according to the laws of different states, a plaintiff must generally show a false statement was published to a third party, causing damage to the plaintiff's reputation or tending to dissuade others from dealing with that person. It doesn't matter exactly which forum the speaker chooses, so any nook of the Internet where a third party can read the statements is good enough.
Moreover, some states consider certain statements to be "defamation per se," which means plaintiffs don't have to prove they actually suffered damage. For example, saying someone is guilty of a crime or incompetent in his or her profession may be assumed by the court to damage that person's reputation.
ETC.