I have been using various Agile methods for over 8 years (DSDM, Scrum) with lots of success, but recently my focus has changed to considering the impacts of adopting Agile in organisations.
Agile is growing up - it has solved a lot of the problems at the technical team level but many projects still hit problems. Most practioners have hit these problems before, for example - how to reconcile the flexibility of agile with annual IT budgets - how to reconcile a fixed price contract without agreeing a set of requirements to deliver etc.
Craig's book helps answer a lot of these questions, and also discusses the issues of scaling agile to larger teams, products, organisations. Most importantly the book introduces some excellent techniques that not only deliver a deeper understanding of Lean principles, but also give solid techniques and examples of applying them in companies.
My only criticism is that this book has a companion book which isn't released yet.