I'll stir the pot: This nation was built on the rule of law. If someone violates the law and it becomes known to you, it is your responsibility of a member of our society to do something about it.
I've got no problem on people reporting illegal activity such as importing engines that are not EPA compliant.
You shouldn't have to worry about being "narced on" if you aren't doing anything wrong. If you are doing something wrong, it is your fault and not the fault of the person who brought it to the attention of authorities.
ZEVO, thanks for the links.