a 6-7 months ago, as a side project (which I never got around to finishing) I was trying to build was something like this. Actually, when I pitched the idea to my friends, the line I used was "rap genius for code". (was trying to annotate huge open source projects like the linux kernel) So the second I saw this post the first words I said to myself were "fuck! I should have finished it".
But this is great!