I've read quite a few books on PKI now, one of the best being Schneier's Secrets and Lies, which is fairly negative on the technology over all, and appropriately so.
This book is a good deal more positive on the technology, but is not pollyanna. I think that Schneier realizes that the technology is a helpful tool, though it does not solve the human engineering problems that need o be solved to implement "real" security. This book helps you understand how to do that, and gives you a feel for where the bodies are buried.
The biggest skeleton in PKI's closed has always been authentication, which PKI does not solve, but vendors would have you believe it does. This is the first book by from a PKI house that lays those cards on the table. OF course, RSA *does* make most of its dough from selling securIDs...
But I think this one is a keeper.