Interesting Proposition: Is Ignorance Ever a Defense?

People are not supposed to get "let off the hook" when they commit a crime, even when they didn't realize they were committing a crime. The reasoning behind this was sound - before the number of crimes on the books skyrocketed.

There have been multiple attempts to count the number of federal crimes, including by the Department of Justice, and no one has yet succeeded. Title 18 of the United States Code, which governs crimes and criminal procedure, has over 6,000 sections, and it is estimated that there are more than 4,500 federal crimes and over 300,000 agency regulations containing criminal penalties. And of course this does not include the dizzying array of state and local criminal codes, ignorance of which is practically assured but still not excused. ...

Think federal prosecutors would exercise their discretion to prevent miscarriages of justice under such obscure laws? Think again. Contrary examples are as numerous as they are horrifying.

Have you ever accidentally run afoul of criminal law? What happened?