I received in the mail my pre-ordered copy of Pro Drupal Development Second Edition yesterday.
The book is a brick. 667 pages with the index.
AHAH is covered but the example provided is lame. It does not cover modifications to a form... Well it does, but you only inject some text in a field of type markup, so you do not need to fiddle with the cached form, or even read anything from it in the callback function. (The callback function is the PHP function that 'writes' the JSON that's returned to the browser...).
The book does not even show one case where Drupal.t() is used. That function should have been mentioned at least.