I assume you all know about the FBI and their 'Carnivore' program which spies on people by sniffing their computer packets and uses this ill-gotten information to get guys in trouble. Some fellows in New York City developed their own Carnivore thing based on information taken from FBI files. Don't ask me how they got into the FBI files.
If you administer a computer network at your school or company, I don't see any reason why you couldn't use this in the routine course of your duties at work, etc. Just use this tool in an ethical and honest way, as all guys do when they use their computers; the way the government does its business. Patrick said it should make a good worthwhile project for readers this weekend.