This is quite good. Actually, as far as design patterns applied to ActionScript with Object-Oriented principals go, this is the bomb.
It's nice to see a design pattern book written using ActionScript as the targeted language. No more reading books targeted for C++, C#, or Java, and try to apply them to AS2. This is especially meanful to cases where ActionScript has no equivalent syntax.
While the book is targeted for AS3, it is equally applicable to AS2. The principals are the same.
It's also nice to finally pick up a book that calls itself "Advanced ActionScript" that indeed talks about advanced topics. Recommended.