I took the JPA Certification Exam today (1Z0-898) and got 84%
I started reviewing using the ProJPA book. I have no real experience using the Java Persistence Api so this book helped me kickstart my review. But the book alone is not enough. I opened the OpenJpa examples in my eclipse and started to play around with it. After getting a feel of how JPA works I used the simulation exam of Enthuware. I highly recommend Enthuware, the questions give you a very good idea of how you will be tested. Without this exam simulator and a good tutor, I wouldn't have made it.
Oh and another important note: The exam objectives in the oracle website are useless. There are topics included in the exam that were not listed in the objectives like Cache and Cascade