User Stories Applied is an excellent guide to writing User Stories and understanding how they can be best incorporated into the development lifecycle. The book is clearly written by an author who has not only an obvious wealth of experience in agile development, but also the ability to provide information to the reader in a simple effective manner.
In the first part of the book, the author provides a good overview of user stories, including detail on writing stories, gathering stories through user role modelling, writing stories when you do not have access to real end users, and testing user stories. Each chapter concludes with a clear summary, followed by an outline of exactly what the developer and customer are responsible for, clearing up any ambiguity.
The second part of the book covers estimating and planning, whilst the third part covers frequently discussed topics, including excellent chapters on bad user story application and using stories with Scrum. Again, these sections are very well written and offer both good explanation and practical advice.
The fourth part of User Stories Applied describes a comprehensive example, bringing together all of the earlier material. This works very well, giving the user extra confidence in the material, and a chance to revisit the concepts again.
Overall, I think that Mike Cohn has produced a great book in User Stories Applied, directly tackling an area that is often condensed and confused elsewhere. Requirements gathering is more important than ever today, and I would not hesitate in recommending this book because I am confident that the guidance it provides will help to produce better software.