This is a great book. It is a thick volume, chock full of information on Macromedia's great Flex product... no screenshots, lengthy code listings, or other "fluff" some authors use to make their page count.
What it does have is detailed, step-by-step guide information on getting off of the ground with Flex, complete with a real world application example and downloadable code.
The only caveats I offer are:
1. This book is not for beginners. You should have previous experience in both object-oriented programming and HTML/XML prior to grabbing this one (though you don't necessarily need to be an expert).
2. If you don't know ActionScript 2.0, go ahead and buy a good ActionScript 2.0 book at the same time. I recommend Colin Moock's 'Essential ActionScript 2.0'.
3. This volume is for Flex 1.0. Flex 1.5 is already out, so the examples as printed in the book will take tweaking, though most of the tweaks are minor and well-documented on Macromedia's web site. As of this writing, the authors are updating the downloadable code examples to Flex 1.5.
4. If your looking for extensive coverage of Charts, you won't find it here (Flex 1.0 did not ship with Charting, though that is available in Flex 1.5). You'll have to figure those out independent of this book (as of this writing, this is the only book on Flex, so you'll have to rely on the docs that ship with Flex and what you can find on the web).
Bottom Line: Highly recommended if you want to learn the ins and outs of Flex.