I have been playing around a bit with a new website, HapYak, which allows students (and teachers) to annotate videos.  My hope is that students who want to learn by watching a YouTube video will instead of being passive watchers, develop an online way to become an active learner.  Traditionally, one would listen to a physics lecture and take written notes.  Now, one could watch a YouTube video and mark it up with Speech Bubbles using HapYak!