This text (which I'll refer to as P) is one of the better WCF books, but there's plenty of room for improvement. The other reviews have plugged a lot of the strengths, so I'll keep this brief.
The real way to review this book is to compare it to the other leading title (Resnick's Essentials of WCF, which I'll call E). Since both books are missing a lot of information, but are in some ways complementary, if you read both, you get about 75% of the basics.
Organization: E is uniform and iterative, and provides introductions and summaries for those who read systematically. P is uneven and non-iterative. Some P chapters are strong, but E looks as if someone consciously went through the entire book with a fine-toothed comb (so to speak).
Transactions: E barely treats transactions, but P dedicates (IIRC) a chapter to them and takes a stand on using them in the design guide.
Hosting: The P hosting section is weak, and the coverage of WAS (which the author recommends for W2K8 deployments) is seriously deficient. Properly hosting and tuning a WCF application is half of the battle, and that battle is almost entirely left as an exercise for the reader. E does a much better job of explaining hosting, but, unfortunately, is also deficient in coverage. OTOH, P has an introductory section of using service host factories to gain some programmatic control over hosting from inside the app, something that E ignores. P also includes hosting advice in the nice guidelines section at the end.
Design: The P design standards section is a nice checklist, but it's not argued properly and it's difficult to find the rationale for some of the points made in the text. OTOH, E doesn't have anything like this. Anyone can read the MSDN/P&P literature on creating WFC services; what readers really need is an informed explanation of how to do it correctly. P takes a stab at it, but E doesn't. Neither text covers other important topics like testability, flexibility, and maintainability as they relate to WCF programming. Both books treat SOA and integration very superficially. P takes a basic stand on good contract design, but E doesn't.
Solution structure/VS project templates/etc: Neither book does a good job covering the different templates (WFC app vs. WCF service library), or how WCF layering should take place. P advocates putting "service logic" in a DLL, but that's about it. E ignores the topic.
Until the next version comes out later this year, I can definitely recommend getting P, but would also recommend getting E to fill in some of the gaps. It would be nice to see not only Lowy expand the design principles section, but maybe also make proper design a first-class component of the book (or maybe even publish an "Effect WCF" book).