This article over on The Three UC Amigos blog gives a great comparison of OCS 2007 R2 vs Lync 2010, both on-premise & Online versions: http://blogs.technet.com/b/ucedsg/archive/2010/11/09/should-i-deploy-lync-server-2010-on-prem-or-wait-for-lync-online.aspx
Loryan Strant, Microsoft 365 MVP
Consultant, writer and speaker