As a Usenet discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one. The Law is generally used on Usenet as an indicator of whether a thread has gone on too long, who's playing fair and who's just slinging mud, and who finally gets to "win" the discussion. It has, over time, become the closest thing to an impartial moderator that Usenet can get. So, what this means in practical terms:
If someone brings up Nazis in general conversation when it wasn't necessary or germane without it necessarily being an insult, it's probably about time for the thread to end.
If someone brings up Nazis in general conversation when it was vaguely related but is basically being used as an insult, the speaker can be considered to be flaming and not debating.
If someone brings up Nazis in any conversation that has been going on too long for one of the parties, it can be used as a fair excuse to end the thread and declare victory for the other side.