I recently received a review copy of the book "Xen Virtualization" by Prabhakar Chaganti (Packt Publishing) and finished reading it a few days ago.
The subtitle "A fast and practical guide" is a matching description - I managed to read the ~130 pages over the course of a week. The book is by no means an exhaustive reference manual, but it gives the reader a good overview about Xen and assists with performing the first steps and getting started.