How do we do this - be careful and strategic with the selection of authentic audiences. With the initial use and conversations about students blogging as a way to cultivate an audience, I have found (and read of the same experiences from others) that finding this audience is much more involved and difficult than simply posting or sharing ... who really will read. How did you address the audience for your students?
In looking at the media aspects as well - there is a conference proceedings from Zahn et al.(2009) that has a nice diagram illustrating the interactions when students are learning through design and creation of the media content that situates the audience, learner, and tools. As an aside, link to the paper - http://dl.acm.org/citation.cfm?id=1600138