The title of the book is probably not going to mean much to many people, but the book is about how you can use existing applications to underpin an 'Enterprise Service Bus' and then build new applications on top. In short: add services (possibly, but not necessarily web services) to your existing applications, then by choreographing these services together build new applications that span several existing packaged application areas. This concept will probably be familiar to people who have worked with Enterprise Application Integration (EAI) tools, such as SeeBeyond, TIBCO and others, though PCAs are more than just integrating existing applications. The aim is to do more with your existing applications, because in today's environment you probably can't afford to replace them.
The book is different from the usual O'Reilly book, it's quite short, and aimed at executive/ senior IT manager type level. There is very little technical detail or hard facts in the book.
The book makes a good case for explaining why the PCA concept is important, looks, a little briefly, at (1.43)alternatives and explains why the author thinks PCAs are better. There is most of a chapter on the case against PCAs, though for my money he missed one important snag - doing this stuff well is difficult, and there are going to be some expensive mistakes made in some enterprises.
Having explained the background and argued the case, the book moves on to work though the vision, creating the service bus that underpins PCAs and what PCAs can actually do for you, and where they are best used. This is the point at which I expected the book to give me a few more tangible ideas and rules of thumb, but unfortunately it sticks to very high level concepts, and I found myself desperate for some more solid detail.
Overall an unusual book - it makes a good job of a high level explanation of PCAs, and why they are important and probably a coming IT fashion, but for me was a bit too light on the practicalities, so just misses a 'recommended'. However if you are looking at EAI tools, and implementing services on top of existing applications, but wanting a high level view without technical detail, this book is certainly worth considering.