Having read my fair share of PMO books, most of which seem to regurgitate the same information and come across as a showing the PMO holding a big stick to beat project managers with, I found Mark's book extremely refreshing and insightful. Our PMO is relatively established and we lived through many of the pitfalls Mark outlines and fortunately survived. I would look at this book as a tremendous guidebook for those starting a new PMO or for those that are looking to "refresh" the vision and mission of their PMO.
While the author does an excellent job of describing each topic by itself, the case studies written by others were the most valuable in my opinion as they brought different points of view from various industry practioners. The "in the trenches" feel was extremely valuable as it was not a theoretical dissertation, but a practical application that weaves in PMBOK best practices where appropriate.