As a Usenet discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one.
As it has evolved, it has spread to all online discussion, not just Usenet, and has become a guideline that when participants in discussion invoke Nazi analogies, all useful information exchange has ended. 
He has clarified that genuine historical references to National Socialism, in context, do not invoke the Law. It has been observed, however, that improper invocations of Godwin's Law also indicate the conversation has lost value. 
There is even a document called Godwin's Law FAQ -or- "How to post about Nazis and get away with it".