This is really, really cool. If I could make one recommendation, after finishing the tutorial it wasn't clear to me what do next. I want to keep learning more C and about the Ruby source code but it just sort of leaves me hanging.
Thanks wasd. The next thing you could do, is highlight some C and ask the community any questions you have. I intend to keep writing the series, since there's easily enough material there for a book. If you signup for an Omniref account, you can follow the project and you'll be emailed whenever I post new content.
This is an awesome book, and I highly recommend it. Just be aware that very little of the book concerns itself with C. The majority of the book is an excellent tour of the internals of the Ruby interpreter.
Also of interest might be this series of blog posts currently being written: Reconstructing Ruby in C [0]