My favourie part was on message orientated architectures. All the fundamental and sophisticated aspects are very explained. These include: the asychronous nature of message systems, the way you can cluster message ques and brokers, the hierachial naming formats in publish subscribe message topics and the different approaches to reliability (best effort, persistent and transactional). There was also some really good discussion regarding the background and importance of message brokers.
As well as technical concepts there are also some interesting sections on architectural processes, documentation and even my old favourite UML!
This book serves as a very good reminder to the importance of software architecture - especially in enterprise systems. Architectural approaches don't just need to be properly understood, they need to be compared with other approaches especially with respect to the non-functional requirements that are important to your system.