Find what Macs are sharing over your network.
It's still a beta, and pretty light on features, but we've found the free utility, Flame, to be super handy for stuff like snooping out who has Printer Sharing turned on...
Just start Flame to see a list of all the computers on your network that are advertising network services. (If it can, it'll identify the user of each computer instead of giving you the machine's name.) This gives you a quick way to scan the network for who is broadcasting shared iTunes music libraries, web sharing, or other network services. Many times individual users are not even aware their sharing options were turned on.
Source: This handy tool comes from a recommendation by Shayne Sandison in the IT department of Fitch Seattle. Thanks Shayne!