Update: Sept 24 2008
When we first announced the 3rd editions of Programming Ruby and Agile Web Development with Rails and, the ship dates were based on Ruby 1.9 being stable by a certain date and Rails 2.1 being stable.
Since work was started on the Rails book, over 500 new methods have been added to this “stable” system. Rails has gone through 2.1, and they announced, but have not yet released, 2.2.
Rails, version 2.2 has been announced, but no beta has shipped. We need to wait until that happens before confirming the date for the book. Until a short time ago, we planned to release based on 2.1, hence the earlier date for the book.
In the case of Ruby, Dave has been waiting for the feature freeze for 1.9. This should happen this month. Based on that, the release date for the book has been updated to the end of the year.