There is no bright line law here... every state is different. We once had a developer working for us who in 1992 had a server that was unsecure and someone was sending kiddy-porn via it. Of course he is now considered a 'sex offender' and his life is well... over. But what can we do? Everyday you hear a story about a kidnapping and American's are scared, protective, etc...
I do agree that something needs to be done. In fact, I wrote my Thesis on 'The Illegalities of The TV Show To Catch a Predator" I think some of you will enjoy it:
http://stalemelon.blogspot.com/2009/04/to-catch-predator-inv...
-P