Good, but inconsistent
This book has 10 authors and it shows. The highlights for me were chapter 4 & 5, which outline some very interesting advanced techniques, and chapter 8, which has a detailed performance tuning case study. I was disappointed in their treatment of XSL-FO in chapter 9. It's difficult to write about a moving target, but I thought Eliotte Rusty Harold's XML Bible did a much better job, and his second edition will be out shortly. I was also disappointed that the authors didn't address grouping problems (Muenchian grouping, etc.). Overall, the book does seem to target the MSXML platform and goes into a lot of depth with that product, though other products are covered. The book does concentrate on portable XSL and discusses the uses and shortcomings of proprietary extensions. Overall, Professional XSL is a good reference, more so if you concentrate on Microsoft platforms, but you'll probably want to supplement it with additional reference material.