In a nutshell: This is a great resource for any developers working with Camel, and also any developers who wants to learn more about, and indeed leverage, Enterprise Integration Patterns (EIP) within their code.
Camel in Action walks you though the entire process of using EIP within your application, and explains the core concepts behind both Camel and EIP using an amazingly focused and clear approach. You will learn all about messages, routing, transformations, error handling and testing within the first two sections alone. The third section nicely covers all the advanced topics that developers utilising Camel in their day job will no doubt encounter, such as transactions, concurrency, scalability, monitoring and deploying to name a few.
If you're using the Spring framework for implementing your main application then it will be worth having a look at Spring Integration, which offers very similar functionality as Camel, and allows you to implement EIP without leaving your current framework. If you do decide to use Spring Integration then I would recommend checking out the sister book to this one Spring Integration in Action
It could be argued that Camel in Action contains a more logical flow with introducing and using EIP principles, and with Camel in Action the journey through the book feels very much like learning to leverage EIP within your applications by utilising Camel. Spring Integration in Action reads more like using Spring to implement functionality that happens to be based on EIP. This is a subtle difference, and has both advantages and disadvantages. Readers familiar with Spring (and indeed actively developing with Spring) will probably get up to speed quicker with Spring Integration In Action, but developers who aren't familiar with Spring (or who want to learn more about core EIP principles) will ultimately get more out of Camel In Action.
In summary, another great 'in Action' book that is destined to become the definitive reference for Camel, and if you're looking to learn this framework or utilise EIP within your application then you can't go wrong by buying this book.