The ActionScript Cookbook (covering ActionScript 1) has been an essential aid for my Flash development: usually the first book I reach for when I have a question. This new book is thinner, and the reason it is thinner is that "Part III Applications" is not there. That section showed seven complete applications that brought everything together. It was a useful read, a chance to see code in context. However I have not looked at those sections much since the first read. I guess O'Reilly thought the same and that it would be okay to drop them.
At the current time this is the only ActionScript 3 book I have read, and I have not done any serious coding in ActionScript 3, so I cannot say how useful it is when troubleshooting. But it is well written, seems to cover all the important topics, and left me itching to get started on some AS3 coding. It pointed out differences between AS2 and AS3, but I think it will still be readable by someone with no experience of earlier versions of Actionscript.
The first three recipes are specific to using Adobe's FlexBuilder 2. There are no instructions on setting up the free compiler on linux for instance. There is also no coverage of open source libraries (for instance asunit has had an AS3 version for at least six months before this book was published). For that matter unit testing gets no coverage at all.
But those are minor complaints. Overall this is just what you would expect from O'Reilly: a good solid book that every AS3 programmer will want to have to hand.
Buy from Amazon UK here, or Amazon JP here.