The concepts in this book are great for any Actionscript developer and they thoroughly explain solutions via design patterns. I'd recommend this book to any aspiring AS3 developer.
HOWEVER, there is so many horrible mistakes in this book. While the content is awesome, it seems like the editor was plastered when he put this little job together. In Chapter 7, it is almost unbearable. Words are omitted, code is omitted, sections are re-pasted into the book often... it's utterly horrible. I keep finding myself getting upset trying to read this book because so much is left out and so much is repeated identically on the next page!!!
All in all, if you're interested in learning Design Patterns (and they are very useful) buy this book. The content is great, the editor should be fired from the universe.