nine common myths about YouTube policies. It's an informative list that I'd encourage you to view and perhaps review with any of your students that are posting content to YouTube.
One myth that I wish they had included in the list regards downloading of content from YouTube. From my reading and research it seems that you should only download works that have been labeled for that purpose such those labeled with a Creative Commons license. Of course, there are plenty of tools out there on the web for downloading videos from YouTube, a quick Google search will yield plenty of links to tools for that purpose.