A lot of organizations have asked for reporting with Lync Online. Microsoft responded by providing some reports to customers which are now available.
If you Global Administration rights to your Office 365 tenant, you will now see some Lync reports are available. You now can see break outs on the number of sessions for IM, audio, video, application sharing, file transfer, web conferences, application sharing, web and dial-in conferences. This is spread across four different reports. This can be really value information to understand how Lync is being utilized and should probably be reviewed on a regular basis.
Here is a screenshot from a tenant that I created. I literally have almost no data <g> however if there was more, it would be showing. You can look at data by day, week or month.
When you click on the View Table button you see a breakout of the numbers that was being viewed.