I agree that OS projects are a great way to learn, but I don't think that most people would be able to _start_ coding from an open-source project.

I found it really useful to look at Ruby projects on GitHub after reading a book or two: I wouldn't even had known where to begin if I opened up a GitHub project on day one.

YMMV, though–I've always got the sense that PHP would be an easy language to jump into and begin hacking on. Same with the classic HTML/CSS/JS stack, which this project focuses on. Maybe it's a language-dependent thing?