I was going to purchase the book, but decided to find it in the book store and give it a browse. After about 20 minutes, I decided not to purchase.
The book may be ok for beginners, but it lacks in technical depth. Once you read about the history of virtualization, the various versions of Xen, and the GUI install, you are half way through the book. There is also very little in terms of reference material, so it's really just a one-time read.
Xen development is moving at a fairly rapid pace, so the book will soon be dated. I can't recommend it to anyone except those without any *nix or virtualization experience.