Matt addresses the book to web designers and developers who are familiar with Drupal's basic operations. For example, the book does not include yet another Drupal install howto, but does provide a useful short review of Drupal essentials, from blocs to Firebug, to the Theme Developer module (chapter 1).
Developers should find everything they need in the book to create dynamic interfaces. There are good explanations of Drupal behaviours, Ajax (with JSON), the translation system (client side). It also includes good examples on how to create a jQuery plug-in.
Technically, the examples provided are realistic and useful. They do not try to reinvent the wheel and the examples make use of useful third party
projects. For example, a "new comment notifier" which is use to describe how to create dynamic events with Ajax makes good use of the "Views datasource" module. The sample code is technically correct and encourages the use of good programming practices.
Those who are not advanced programmers will get a good understanding of the code since the examples are usually shown in their full form, then the author cuts the code into smaller pieces to explain each concept in detail.
Overall, this is a useful book and a good reference. Aiming at experts, it is a good reference guide for people who are already familiar and work with Drupal. It is not one of the beginners' books, which can be found everywhere, but a good comprehensive guide for a more advanced knowledge building.