Don't worry we wont narc on you and we will even help you to find out who on your network is listening to your tunes. When you go to close iTunes down and it yells back at you that someone is connected to your library - what do you do?
Leave it open so they can continue to get their music on? Close it even quicker because the concept of sharing scares you? Look to disable sharing all together?
Either which way this simple dos command will point you to who is listening to your music.
You will see something like this if you have someone connected to you:
Now you can make an educated decision depending if its Bouncy Betty in HR or Smelly Mark in Editorial... :) It attempts to resolve net-bios names but that doesn't always work. But hey an IP is as good as a name around my office. And here 192.168.1.108 is a fugly intern. Can you guess what I did?
Update: Apparently there is an installable app that will do the same thing on Windows or Mac. Check iTunes monitor out here.