I've released a new version of the Ruby on Rails Tutorial book to bring it up to date with the recently released Rails 2.3.6. The differences are essentially cosmetic—amounting to little more than changing occurrences of '2.3.5' to '2.3.6'—but it's part of my commitment to change the tutorial as Rails itself changes. Readers shouldn't have any problems with the new version (at least, my test suite still passes), but please let me know if you run into any trouble.
Of course, the upgrade to Rails 3 will require more extensive changes to the book, and I plan to turn my full attention to that task soon. Expect to see a Rails 2.3.6 version of Chapter 12 drop some time this week, with an updated Rails 3 tutorial available around the same time that Rails 3 ships, probably around a month from now.