You'll want to pay special attention to these if you are running the evaluation version of OCS 2007 R2 or Communicator 2007 R2.  You can read more about it here:

http://communicationsserverteam.com/archive/2009/06/10/523.aspx

and here:

http://support.microsoft.com/?kbid=972041
http://support.microsoft.com/?kbid=972042