Arriving at Rails after a career in finance, it was especially important for me to find a book that took a holistic approach to developing Rails applications. Mr. Hartl's book does an exceptional job of addressing both the structure and function of Ruby on Rails, as well as the most modern methodologies for developing web applications. Without this book, a novice web programmer like myself likely would have missed learning test-driven development (TDD), which is critically interfaced with producing robust applications.
Mr. Hartl has also put together an outstanding series of screencasts, comprising over 15-hours of video, providing an inside look into an advanced user's coding process. The screencasts pay dividends well above their investment of time and money.
A cursory examination of Mr. Hartl's resume, including his teaching awards in physics at Caltech, will evidence his great talent for simplifying the complex. Having explored this book among a half-dozen of its peers, I can attest that it is indeed best-in-class.