With our upcoming Office365 cloud service, Lync Online will be a part of the offering. I have had a few education customers ask me what the differences will be. I found this useful matrix (note: this is a Lync Online beta feature matrix and subject to change):
From the Beta Lync Online Service description document here. Note: there is also a matrix for Beta Exchange 2010 Online vs. Exchange 2010 on prem comparison matrix.