This review of Vidbolt came through on the Chronicle of HE's ProfHacker site recently. It enables you to add comments to YouTube videos - see the example, which seems to be a transcript, but there is potential for a lot more.
http://chronicle.com/blogs/profhacker/annotate-video-on-the-fly-a-review-of-vidbolt/56787
"Vidbolt is a social video platform where you can: add / bolt comments to a moment in the video timeline, see comments from your friends and people you follow using our comment filters, get a visual snapshot of what people find interesting using our Vidbolt
heatmap, and see your comments integrated with the video."
https://beta.vidbolt.com/