Well the threat of the trusted insider is no urban or IT myth. It is very much real, and everpresent. Though it is tough to get statistics in relation to actual computer crimes committed by trusted insiders, it is safe to say they are under-reported. What can you do though to mitigate this? There are steps that one can take. First and foremost in my mind is having periodic audits by external ie: third party, network security personnel. While not everyone can afford to do this it will go a long ways towards keeping everyone honest. Secondly, one could also have their internal network traffic analyzed on a regular schedule. This is both cost effective and also helps diagnose the state of your network ie: any viruses, worms, malware, or other shady business going on. It is something that I for one, certainly encourage my clients to do. Food for thought.