I just put up an interactive javascript tutorial. It starts simple then builds up to passing around functions, closures, continuations. Give it a try and let me know what you think. http://nathansjslessons.appspot.com/
Nathan, great tutorial! This is why I love HN. It reminds me of some of the interactive Ruby tutorials I've done. You've really got something going here.
I went through half an hour before I read your comment. My internet is a small world. And I liked it.