Today I've taken the JPA 2.0 exam and successfully passed it with 93%.
My learning process began in September '11. I've read whole "Pro JPA 2.0 Mastering the Java Persistence API" by M. Keith and M. Schincariol and then proceeded to the JPA 2.0 FR specification. I've had some experience with Hibernate (ca. 1,5 year) and was using it quite often. During the reading time I've tried to read and answer to some of the StackOverflow questions. I must say that it was a great practice, as it forced me to reread some of the more difficult part of the specification and confront it with the real-life scenarios.
I've also used the JAVA-KATA website by Andrei Bodnarescu which holds some interesting information.
But, as usual, one of the most important parts of my preparation was the Enthuware's mock exam simulator. I think it's definitely worth its price, it consists of a great number of very high quality questions which reflects topics you're tested on during your exam. Really - read the specification or some book and do some Enthuware mock questions - it'll be definitely enough to pass this exam.
If it comes to the exam itself, there were no surprises. There were only 6 questions on the Criteria API (which was the hardest part for me). A lot of questions about locking and about using Maps. As usual - some of ugly Oracle mistakes like bad line wrapping, additional characters put which would make the code not be compilable or using unexisting annotations (e.g. @ID instead of @Id). Some questions were about EJBs transactionality and L2 cache. There were no questions about advanced L2 Cache like CacheRetrieveMode or any of this stuff.
Another material that can be used as a resource to prepare for the certification exam ORACLE CERTIFIED EXPERT JEE 6 JPA is the following android app:
https://play.google.com/store/apps/details?id=org.jpaexam It is basically a quiz about the JSR 317: Java Persistence API, Version 2.0 Final Release.
This app can be used as a resource in learning the JSR, but also for those who are preparing for certification, both in the initial period (to assess the challenge), as when more advanced (as a simulated pre-test).
This address the following topics: Entity Class, Persistent Fields and Properties, Access Type, Primary Keys and Entity Identity, Embeddable Classes, Collections of Embeddable Classes and Basic Types, Entity Relationships, inheritance, EntityManager, Entity Instance's Life Cycle, Persistence Context Lifetime, Locking and Concurrency, Entity Listeners and Callback Methods, Bean Validation and Query APIs