For this post I am logged on as a regular user without any Administrative credentials.

Just type a name and Join the meeting

The Lync Web App wants to download/install an HTML5 plugin to enable Audio & Video

Run the application as a regular user, no credentials are request and no UAC dialog is displayed.  The plugin just installs

Joining the meeting

You have to add the URL to the trusted sites or admit it every time (your choice)

Joining to the meeting including Audio

This is awesome, no credentials required and any user can join Lync 2013 meetings with all functionality without requiring a full client or admin credentials.
I bet this will hurt Webex hard!