I'd have to agree with Reddy.
I'm taking the test in a few weeks time. I've not felt comfortable with my performance in mock tests and Sun's prep test. Once I started reading the specs, I've felt a lot more comfortable.
MZ's notes are based on the specs, but I think it's well worth reading the specs carefully first, making sure you understand them fully and then using MZs notes as a refresher.
I've found EJB3 In Action to be an excellent book for learning EJB3. Once you have grasped the concepts, then the specs are actually not too bad to read. The specs will fill in all the gaps - very comprehensive.
I have needed to use Apress Pro EJB for its fantastic coverage on Transactions and Persistence Context. I've found that area so confusing and fustrating. So many different permutations of bean vs contrainer transaction demarcation, JTA vs Resource Local transactions, whether or not persistence context is propagated, when to use JoinTransaction(), what happens when you encounter application vs system exceptions ... aagggh. It's still not 100% clear to me, I expect to get the odd question wrong in this section.
Since I'm a Business Analyst and not a programmer, it's more important that I understand the general concepts. I'm happy just for a pass, and I know my development team will appreciate my efforts to better understand their world (they better ... it's been really hard work !)