Increasingly, there is a growing corpus of Django reference material being published. But most of the books target introductory to intermediate usage of Django. Long-time users with several successful projects under their belts stand to gain very little from these books. "Pro Django" is the book to read when you want to move beyond this.
Rather than covering every aspect of Django's internals, "Pro Django" starts with advanced Python practices (including a excellent introduction to metaprogramming) and then targets the major subsystems of Django, providing what is essentially a roadmap into various portions of the implementation. Major details are well covered and helpful hints are given about where to look for more information.
Beyond that, many chapters (particularly Chpt. 7) provide insight into good practices for all web developers. Details about HTTP handling, sanitizing data from users and ways to build "pluggable" backends are topics that extend well beyond Django's borders.
For developers who want or need more out of Django, this book makes a fantastic complement to the source code itself, providing the "why" of how Django is put together. There are many great examples provided throughout the book that include ways to take advantage of existing functionality or build your own custom solution.
The chapters themselves were well organized, clear and build upon each other as well as disparate portions of Django could be tied together. This is definitely a book to read through to the end, as the final two chapters tie the book together and provide some exceptional code that could benefit many different projects. The writing style was friendly, conversational and well-done. Rare was a typo or other mistake.
My only complaints may be the first chapter and occasionally a lack of code. The first chapter treads what seems like the same tired grounds as many other books as to the overall architecture of Django. As to the lack of code, the Models chapter felt light on code when reading it, though there is still quite a bit there.
All in all, I highly recommend this book to anyone looking for a guide into the depths of Django.