This was a question from a school district in Illinois. They wanted to prevent the students, hosted in OCS, from finding management via a search in OCS and accidently IMing/video chatting with them.
There is an ethical wall sample script written for OCS 2007 that still works with OCS 2007 R2 and is based on OU membership. You would essentially place your upper management accounts, etc in one OU and students in another OU to provide isolation in OCS:
There are also more robust 3rd party ethical wall add-ons for OCS from FaceTime, Akonix & Symantec that provide this functionality as well.