The next beta will include a chapter covering Active Record (roughly covering what was in chapters 18 through 20 in the previous edition). It has been significantly reworked, streamlined, and updated to reflect the arel changes. This is a big piece of work, and I’ve completed the first draft, it has been reviewed by the editor, and I have her review comments back.
What I am mostly waiting on at this point is news as to when (or if) the Rails 3.0 RC release will be made. Word is that it that the Rails core team is wrapping up everything at this time, but if the release isn’t made by this weekend, I will push out a beta early next week.
Thanks for your patience.