The Rails 3 Way is an interesting book representing a large amount of effort digging into Rails 3. It shares insights and technical knowledge you'd struggle to patch together from blog posts and documentation. It's a very opinionated book and will not be to everyone's taste. For starters, ERb isn't covered at all, instance variables in views are scowled at, and Test::Unit is treated with contempt.
It's not an introductory book in any sense and Obie acknowledges this in his introduction. Obie bills it as a "day-to-day reference for the full-time Rails developer" - a fair description IMHO, but the book feels disjointed in places and has a scattershot approach to what it cares to cover. You need to be clued up to digest this book properly. For an intermediate to expert Rails developer (especially one yet to move to Rails 3) or an expert Rubyist new to Rails, The Rails 3 Way is a useful book that unearths some of the trickier parts of Rails 3 a professional needs to know about. I recommend it - but not as wholeheartedly as the original edition for a number of reasons:
* Parts of the book feel curiously short or scattershot in their coverage. The AJAX on Rails chapter is a mere 16 pages. The RSpec chapter is 33 pages long and provides only an overview (and says as much) though given the recent release of RSpec 2.0 and the new RSpec book, this may be a plus. Rails Engines aren't discussed or covered at all except for a small sidenote that links you to a gist on GitHub. It's not all bad though - some chapters are great, complete guides to a topic, such as Active Record Associations and Advanced Active Record.
* A lot can be gathered from what's not mentioned in the book at all: Capybara, Selenium, Webrat, Searchlogic, SASS, factory_girl.. It wouldn't be expected for a book like The Rails 3 Way to go into depth with any of these tools but having no mentions of them when related issues are raised feels like a missed opportunity to give people some guidance. The lack of Webrat is bizarre since the only full integration test shown in the book clearly uses it. Webrat is neither mentioned nor explained. Nor is Capybara, Webrat's heir apparent.
* The concept of using a different ORM than ActiveRecord is mentioned only once, in the context of running --skip-migration on a rails generate in order to prevent ActiveRecord migrations being generated. Considering what a big deal ORM agnosticism was when developing Rails 3, this is a disappointment.
* Concepts are sometimes used in code but not mentioned in the text. In the RSpec chapter, for instance, the first example includes a call to factory_girl's Factory method, yet nothing about factory_girl or the benefits of factories is covered. I only know it's factory_girl being called because the gem's name appears in the copy-and-pasted output from running bundle install 500 pages earlier.
* Tests are rarely used or demonstrated except in the RSpec overview, Working With Active Record (4 test snippets in 39 pages), Action Mailer (once), and Active Record Associations (6 test snippets in 50 pages). Oddly, though, 4 stray instances of using Test::Unit instead pop up when writing a test for a belongs_to association - it's never used again anywhere else in the main part of the book..
Nonetheless, I recommend the book. It's a flawed champ. While there are other great Rails books in the pipeline, The Rails 3 Way offers a lot right now, as long as you're either happy to look past its flaws or skilled enough to mentally fill in the blanks..