I am SCBCD certified, I passed with 85%, a huge relief.
1) I had no prior EJB experience. I used EJB3 in action as the introductory book, very well written book for newbies.
2) I followed the SCBCD forum regularly, it was a very valuable tool in the preparation. There were a lot of questions that I never thought of and there were a lot of helpful people answering them. For a lot of questions, I would code a simple example and see if I could make sense of it.
3) Enthuware definitely helped me with mock tests, I did not do very well on their mocks, 75 was my highest and I failed on one of them. I used it to identify my weak areas and study those a little bit more, I would refer to Specs, MZ notes and other internet resources. I had all kinds of problems with JPQL and EJB roles, I still think they are my weak areas.
4) I rererred to specs selectively for areas like Operations Allowed tables, Exception tables etc.