After the mock exam in Head First EJB, the real exam was easy. I missed 7 question, but one grag-and-drop question I simply could not answer due to "Out of system resource" the application was given. To recover from the system failure I even had to change the computer.
I had some try-and-error experience with EJBs, so for the preparation I only went through the Head First EJB. I guess the point is to understand reasons for every element in EJB architecture and dependencies among them. The SCBCD forum is a great help as well as HFE errata pages on the o'Relly site.