I've never seen one done quite like this. It would be a neat addition to the wiki, perhaps a group one. It does what Diigo does, along with many other sites, but this seems laid out very conveniently.
For those thinking of using dropbox with your students, here is a quick tool that allows you to make forms that are deposited into a folder in dropbox!
What about the use of cell phones in class?
bic - 11 Oct 2010 - 11:00:10
Now this is my opinion, but they're not big enough. Nicholas Negroponte says that students should not be learning about their works through a keyhole... - dfw