I've also been a long time Emacs+Org mode user, and while I was aware of babel and the ability to tangle literate programming documents, it simply never occurred to me that I could execute those snippets in-place and manipulate the results in-place like an ipython/jupyter/mathematica notebook.

I had the same reaction to that post, and I'm really excited to get more familiar with it, as it makes a great addition to some of the work I'm doing now.