It is an O'Reilly bookAnd why is this important? Well, because I think O'Reilly books are often good. They tend to be concise and to the point, this one too. Not one of those heavy-weight, 1500-pages ones, which actually does not tell you much more, than a shorter, well-written one will.
General ReviewThe authors do a good job of introducing flex2 in the history of flash development. You gain a solid understanding on how the platform works and how to leverage it. If you now nothing about flash/flex development, this book will get you up to speed quickly.
One really nice thing about it is, that it is tool-agnostic. It tells you about FlexBuilder yes, but it also explains how to use the command-line compilers. All of the books examples are free from IDE-ties.
Detailed ReviewAfter an initial introduction to the platform, the book continues with the following overall subjects:
MXML / ActionScript
A quick and informative explanation of what MXML and ActionScript is, and how they relate to each other. If you know programming in languages like Java or C#, you will quickly grasp how to program ActionScript and what the ActionScript language provides.
User Interface Chapters
It then explain how to build rich, interactive flash user interfaces with flex2. It comes all the way around, telling about all the UI components, containers and layout management, view state management, media management, effects and transitions and more advances stuff like modal dialogs, drag-n-drop, cursors, customized appearence etc.
Business Logic Chapters
I call this part of the book "Business Logic Chapters", because they handle the stuff you need to know to put logic behind the UI. This includes data models for the UI components, validation and formatting and various ways to talk to servers.
The Other Chapters
In the end, there are some extra chapters on debugging and on how to build components for reuse yourself.
ConclusionIf starting up on learning flex or if you want to quickly grasp what flex/flash can do for you in rich internet application development, this book is for you! If you already program in flex2, you most likely will get informative stuff out of the book too, but you will also be skipping something.
All in all I enjoyed reading the book. Well written and informative! Recommendable.