Never seen the point. Every time I've riden in a car with someone who had one there are so many false positives they just ignore it.
Cops around here are more concerned with squids doing wheelies than me on my dirty DS. The few times I have been stopped I have been let off with a warning after they see all my paperwork is in order.
If I do get a ticket I have a few friends that are court clerks. Sometimes paperwork just dissappears