As of right now, there are 3 Clojure books available in full (Programming Clojure, Practical Clojure, and this one), and one on the way (Clojure in Action). I can't speak to Clojure In Action, but I've read the first 3, and this is definitely the best one.
1) It covers Clojure 1.2, which is the current version, and has some important differences from 1.0 and 1.1. The new features are pretty cool, but sometimes their purpose is a bit obscure when looking through the documentation.
2) It's so darn specific, while at the same time being very concise. Common sticking points, like the behavior of unquote splicing, are gone over with non-trivial but easily understandable examples. Structural concerns like refs vs agents vs futures vs promises are discussed with good explanations for when you should use each.
3) It explains why things are cool - for instance the explanation of "state" and "identity" in functional programming is one of the best I've seen. If only there was a section on monads, this book would be downright canonical.
Basically, if you're planning on writing Clojure, or you want to see if the language jibes for you, you should get this book.