This is a great book about development. One of the best books I ever read to increase my skills necessary for my job. Not only that all the different possible architecture are described in a very understandable manner.
This book also makes clear, that you do not always need the most complicated architecture. For a simple application, a simple architecture could totally fulfill your needs.
Which leads back to one of the most important principles in software development: KISS, keep it short and simple. Software gets at the end always much more complicated that planned or expected at the beginning. Lot of developers do not fear the complexity of the source code they produce and at the end you get stuck in a messy code, impossible to have the necessary overview.
Once again I saw when reading this book, that many of the architecture, similar to design patterns are used without knowing them by name. Whatever design or architecture you select for your application, important is that you and your team know it and keep coding to the selected pattern.
Fowler also describes in a very clear example the data mapper which is a pattern I created myself years ago out of long experience. Its nice to see that I was on the right way and that a guru like Fowler describes it in a very similar way as we designed it then.