The PDF-book of Dave Thomas and David Heinemeier Hansson has just been updated to Version 2007-5-6. It now covers the newest developments within the Rails development community. Especially the "observer" and "sessions" sections have been updated.
Although I can recommend the paper-version of the book … it’s really great for reading in the park 😉 … Dave and David really show with their PDF-version how to make innovative use of electronic books.
All standard e-books I bought before always made me angry afterwards: The rigid Acrobat-DRM treated my like a potential criminal. And the e-books had no extra features compared with the paper version – only the disadvantages of an e-book.
Dave and David used another approach with their second edition of "Agile Web Development with Rails": Before passing for press of the printed version, they started a beta program of the beta-pdf-version. They collected thousands of suggestions and debugging hints, integrated those into the final (payable) version of the PDF-book and the printed version. In addition, the PDF is linked internally and externally to get code examples and explanations easy and fast. The PDF is personalized for copy protection and therefore you can use your preferred PDF-viewer to access the book. And it’s really great that the authors now update their book to the newest developments and that I as a customer can update my PDF-book free of charge. That’s best practice for e-books!
As regards content, I can really recommend everybody who wants to learn Ruby on Rails. The tutorial part of the book is didactically well put together, great to read and gets the rails basics across. Furthermore it introduces into the coding philosophy of Rails. So, it’s the guidance for elegant code … and it’s at the cutting edge of the Rails development.

Upgrade-Link for the PDF: books.pragprog.com/titles/rails2/reorder
Info & purchase link: pragmaticprogrammer.com/titles/rails/