Hadoop MapReduce Cookbook is a good reference if you already have a decent understanding of Hadoop. It is helpful when you ask "how do I do that again?" or "what is the exact procedure for doing that?". The book does a decent job of explaining how to setup a cluster and basic cluster management, but it doesn't really explain the logic that is going on. While it is easy to understand what the author is doing, if you are new to Hadoop, you will likely get lost and have to reread some sections. This becomes more of an issue with more complex topics.
One of the strengths of the book is how it is broken down into recipes. Most programmers are able to read the code examples and understand what is going on without pages of explanation, and if that is you, the book will probably be very good. However, if you like lots of logical detail before you fully understand a new topic, you will probably find this book a bit lacking. The recipes are grouped logically and do follow a natural progression.
Overall a pretty good reference, but needs more details and explaination to be a good teaching book.