I already knew a bit of Ruby and Rails when I started reading Rails for PHP Developers. After having read Pragmatic Agile Web Development with Rails, THE Rails book, this book presented nothing new to me. It may be a good resource for people that know PHP, but do not know Ruby and need to learn Rails in a urge. The comparisons between Ruby/Rails and PHP are the most valuable content of the book, and you can learn some interesting stuff from them.
Book on Amazon: http://www.amazon.com/gp/product/1934356042