I was a bit worried before the exam since I did not do that well when doing the practice exams shipped with the book 'J2EE Sun Certified Enterprise Architect for J2EE, Paul Allen, Joseph Bambara'. Apart from that I did the two practice exams on www.javaqueries.com. I also read some parts about JCA in 'Mastering Enterprise Java beans' (3rd edition) and revisited my notes from the SCBCD exam from the book 'Head first EJB'. Apart from that I browsed through the Gamma Design patterns book again and paid a lot of attention to the difference between the Bridge and Adapter patterns. There is one excellent link (leocrawford.co.uk) which shows the distribution of questions over categories.
I did not like the Paul Allen book very much. Many inaccuracies, sometimes dead-wrong information, practice questions that are phrased inaccurately. It helped a lot that I already did the SCBCD certification since I don't think anyone would get EJBs from reading this book. The difficulty there was 'going back in time' to EJB 1.1 instead of using EJB 2.0, but this also made it a bit easier. As long as you remember that CMP is only useful for simple data where performance is not required (in the old EJB 1.1 days), then you know when to choose BMP and when to choose CMP.
Now the exam itself. Really clearly phrased questions and when in doubt about for instance the two correct answers, the remaining answers were all plain wrong. I did not encounter any detailed questions about API usage. Looking back, I could have done the exam with a lot less preparation, but it is always better to be safe than sorry.