I just started reading the early beta of Rails for Java Developers. It's a new book published by the Pragmatic Programmers and written by the Relevance guys- Stu and Justin. Perhaps the most shocking thing is that they have time to write a book. I have been lightly involved in the review process for O'Reilly's upcoming "Rails Cookbook", currently available as a Rough Cut. It's a lot of work to stay current with a moving target and make sure all of the code works.
As far as the book goes, I think it really is going to fill a gap in terms of being a reference for people that know how to do something in Java, and want to know what the equivalent thing is in Ruby on Rails. It's like those options in a new version of a product to see the menus for the prior version, so that you know where to find things. Of course, I haven't tried much in the book yet, so I can't speak to it's quality, but I like the tone and the approach so far. It appears to be just over half way to their 300 page target, so, there's a lot to do before Nov.