I've been through the book one time, and I must say it's the best format for a certification book because I really think I "got it" (or got a lot of it). Well, I'm not completely through with the book -- I still have the Appendix (mock exam) that I'm "saving" for later.
The one beef I have is that the chapter-end mock questions seem like an after-thought on several counts. First, they will have questions that ask about things not covered yet (for example, the chapter 6 test had "ejbSelect" and "relationship field", and we hadn't gotten there yet, and the chapter 8 test had java mail queue and java mail message consumer, none of that had been presented). Second, I think it's a major cop-out to put the spec page numbers on the answers. I think if the answers were in the same style as the book, there would be loads of scribbles that reenforce the things learned in the chapter. It would be different if in the chapter it said read this spec page, but that's not the case. Don't get me wrong... I 95% love the book but the coffee crams are an area that can be improved upon, IMHO.