This well-written, lucid and very intelligent book is the perfect choice for those developers who must, for whatever reason, use plone. Far and away the best one out there. It is not comprehensive, by design, but rather concentrates on the 'best practice' elements of plone - zope 3 integration, elegant use of relational databases, well-structured deployments based on paste, integrating version control and so on.
Unfortunately, it is the elegance and clarity of this approach which really shines a light on the legacy inconsistencies, code-bloat, messiness and quirky multiples re-invention of the wheel that characterises Plone as it stands in 2008. By all means, if you are stuck with plone, use this book as a means of smoothing over your pain. But otherwise, it's perhaps most useful and some provocative ideas about how you could use Zope 3 to build new projects, as well as an elegant demonstration that despite plone moving towards coherence, there is a terrifying amount of nasty code out there in Plone that it takes a book this long and erudite to steer clear of. Maybe pick up Weitershausen's Web Component Development with Zope 3 for a similarly intelligent and eloquent, but far less terrifying, read.