As the title says, this is a book celebrating 10 years of Puffy. Most of the book is taken up by Ami and Yumi's recollections of their time together as Puffy, but there's plenty of other stuff. In addition to a somewhat lengthy discussion with Ami, Yumi and Tamio Okuda, there are a number of messages from all sorts of people who have worked with and/or are fans of Puffy: people such as Andy Sturmer, Butch Walker, Kaela Kimura, Pierre Taki, Masamune Kusano, Tortoise Matsumoto, and others.
Additionally, the book has a fairly generous amount of pictures. Most of these pictures were taken explicitly for the book, while the remainder are generally private Polaroids of Ami and Yumi in various places - the oddest of these are the ones in the book's special insert (which you have to cut open with a pair of scissors) that mostly are of Ami and Yumi while growing up. So, if you ever wanted to see a 16-year old Yumi dressed in ganguro style, or a picture of Ami while she was pregnant with her daughter, this book is for you.
This book also has a very thorough discography (even including a few things not currently shown in their official site's discography), as well as pictures and thorough merchandise listings from all of Puffy's tours through the end of 2005.
Oh, and there are mini-comics starring Ami and Yumi sprinkled throughout the book, as well. And unlike most Japanese books, this one reads left-to-right.
If you just have to have this book, YesAsia and Amazon Japan have it to order for around $30.
Other
Several Scans From the Ayumi Book (Click for a larger version):