I wish we could combine all this stuff together regardless of media. I'd use it in a heartbeat to curate class notes and recorded lectures! Particularly with a community this would be awesome, harnessing everyone's highlighting to pull out a veritable "best of" the course, without losing any context!
This program is wonderful, I regularly use it for highlighting and annotating PDFs. Just imagine this with a SoundCloud-like "highlighter/annotator" for AV files thrown in the mix.
There was once a thing called Google Wave which would have got pretty close in it's proto form, and had it continued being developed probably would have allowed this and more.