I don't have much to add over T. Anderson's review, but wanted to weigh in with a 5-star vote as a practicing distributed-systems architect. In particular I'm irritated by the one-star review from the person who obviously didn't understand what he/she was buying.
This is as close as you're going to get to a one-stop "encyclopedia" of patterns relevant to distributed computing (and other areas as well). I own most of the architecture/design patterns books, but this is the one I'll go to first for ideas, study, and use as a reference.
As for content, the catalogue of patterns is more comprehensive than any other volume I'm aware of and it is well organized. Each chapter describes a group of patterns that address recurrent vertical and horizontal architectural problem spaces. Each group is briefly introduced and described in the context of that. These introductions are pithy, on-target, and along with the complete pattern descriptions almost constitute a good introduction to distributed computing in general.
Most patterns are described in two pages in a format that has been well-honed over time for usefulness and comprehensibility. You find out where and when each pattern is likely to be useful, what motivates it, how it works, pros and cons, and what other patterns might be used with it.
The cross-referencing between patterns both within this book and in other sources is extensive and one of its most valuable features. The authors provide you with 114 pattern descriptions cross-referenced with "over 150" from other sources. That's a pretty extensive language!
Lots of spelling errors and such, but nothing that should confuse anyone.
This book is NOT a true encyclopedia, and you will want or need some of the core volumes that cover the "over 150" patterns that are referenced but not described here. The most notable are:
Patterns of Enterprise Application Architecture (The Addison-Wesley Signature Series)
Enterprise Integration Patterns: Designing, Building, and Deploying Messaging Solutions (The Addison-Wesley Signature Series)
Remoting Patterns: Foundations of Enterprise, Internet and Realtime Distributed Object Middleware (Wiley Software Patterns Series)
Most, if not all, of the material in Pattern-Oriented Software Architecture Volume 2: Patterns for Concurrent and Networked Objects is covered in Volume 4. If you don't have that book you might want it for deeper discussion of some of the patterns. On the other hand, the current volume contains important updates to a couple of patterns in the earlier volume.
If you're new to patterns, please avoid Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley Professional Computing Series), also known as the "GoF" (Gang of Four) book. It is a classic and the authors deserve their "props" for introducing design patterns to the broader development community, but it is the worst-written and most misleading book I've ever read on patterns. (In fairness to the authors, it was the "grand-daddy" of them all and perhaps they can be excused for not having the intervening 12 years of experience in pattern documentation to help them.)
I've heard good things about Head First Design Patterns (Head First) and Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and Iterative Development (3rd Edition) from people who have read the GoF book, so you might try that. I haven't read either myself.
If you're familiar with patterns and want perhaps the most comprehensive and useful single pattern book to date, especially if you're involved with the architecture of distributed systems, buy this!
It is not for beginners or those looking for boilerplate code!