In case you weren't already aware, you can also download a zip of the
source code from the publisher's website
it's cheating to start with the finished product but I always end up
making mistakes (typos, skipped lines) when I re-type from the book.
This tip doesn't directly speak to your post, but I'm also working
through r4r and I find that it helps me focus better when I'm not
having to troubleshoot mistakes I've introduced into the code examples.
Overall, I've really enjoyed r4r. I started out with Agile v2 (beta)
but found the organization of the content in r4r much easier to follow
and really felt like I was grasping the concepts introduced. Then
again, I'm a total beginner at programming and rails. Agile is
definitely worth taking a look at, especially the v2 pdf beta as it
covers the latest stuff going into Rails 1.2. I hope there is a new
edition of r4r in the works to bring it up to date, but the current
edition is still a helpful introduction.