I started the Pragmatic Guide to JavaScript earlier today and wanted to share Porteneuve's (possibly novel) approach to teaching despite the inherently moving targets of this subject.
For the basic examples, the author provides six repos: one for each of the most popular frameworks. For the larger, advanced examples, the author codes for one framework, but encourages readers to fork and contribute to the other five.
With innovative, collaborative efforts like this, Edgecase Ruby Koans, and Murphey's jQuery Fundamentals, I am glad to be the last generation to learn exclusively by typing in code from books and magazines. A world with less isolation and errata sheets sounds good to me.
Feel free to share your favorite educational uses of github in the comments. There is obviously much more to this space than microedits and i18n.
http://stratepedia.posterous.com/exercises-left-to-the-readers-teaching-with-g