I am only a beginner in math.se, (and to math as well in some technical ways, not in terms of enthusiasm though) in my view i feel that math.se has a very good amount of wealth of knowledge in math and is rapidly increasing. I think in my opinion, at some point in future it could give math class room courses a run for their money if not atleast act as a very good supplementary material there by helping students at all levels from around the globe in a huge way.
In this view my suggestion or idea is to create some sort of structure to the collection of Q&A's in some sense (something much more than tagging), the structure itself could be subject or topic dependent, which can transform the Q&A collection into some sort of a Virtual Tutor or a sort of a classroom.
I don't know better examples but would like to know if there are any examples or such ideas .