The content seems just great - even in a current work-in-progress state it reads like a solid, proper, well structured and thought out book and not just like a typical set of more or less random posts on HTML/CSS. The presentation wakes a grumpy rebel[1] in me, though =)

Also, I think that having the ability to play with some code and see results right there on the site (e.g., tweak all the included numerous demos) would bring even more awesomeness to the project.

Edit: formatting. (Thanks, saraid216, you are right.)

[1] http://contrastrebellion.com/