Lync for Mac was released in October 2011.  There were some issues around connectivity with Lync for Mac and Office 365 Online servers.  Microsoft has released an update that resolves the following known issues:

  •          Lync for Mac sign-in into Office 365
  •          Installation of Mac OS X Lion 10.7.2 causes Lync for Mac to become inoperable

If you are experiencing either of these issues, you can download the update now or wait for the update through Microsoft AutoUpdate. For more information on these issues please see the KB at http://support.microsoft.com/kb/2634523.