I took all lessons yesterday, and completed the problem.
I found some UI glitches (% of classes completed), and I think that the UX can be improved by highlighting at any point which lessons/exercises are not done yet - rather than simply highlighting how many are left.<p>The problems are valuable, and I enjoyed solving them. I think that you might want to show multiple alternatives for solving the same problem - that's one of the cool things about Ruby.<p>I would love to find something similar to HTML/CSS. I know that codeschool have an HTML5 one, but unfortunately, I need something more basic :)