Simon Chappell has written up a very nice review of PMD Applied. He has some kind words regarding the "currentness" of the book:
After having been out for a year, the exact level of the software described in the book has been passed by. This may bother you, but I feel that the basic principles of PMD have remained true and so I wouldn't let the version numbers dissuade you from purchasing.
Yup, I hope the book's still useful to folks wanting to learn more about PMD; with the recent XPath rule speed improvements, the notes on writing those types of rules should be even more relevant. Enjoy!