I passed the OCAJP 8 exam yesterday with 88% score. I was not at all happy with the score since I knew I could have done much better. Here is some information that I can give out from my experience:-
How I prepared?
I spent around two weeks to prepare for the exam. I work a job, so I could only study during the evenings (around 3-4 hours every evening). During the weekends I could study more. I read the OCAJP 8 study guide written by Jeanne Boyarsky and Scott Selikoff thoroughly. And I revised the chapters a few times to make sure I remember all the concepts well. I did *not* do any practice tests at all. I only attempted the questions in the book at the end of each chapter. It has like 20-30 questions at the end of each chapter, and a total of 6 chapters.
A little harder than I had expected. But it was easy in general. Of course my score doesn't reflect that I found the questions easy :-). That is because I messed up my time management. I was very slow. For some questions I was quite sure of my answer, but I still checked it like 2-3 times just to see if there isn't a hidden trick that I had missed and that I had read the question well. This is something I should not have done. The result was that I just finished the exam in time. I had only 5 seconds left after having answered the last question. During the test I marked around 10 questions for review, but reviewed none.
The exam is easy in general for people who are already familiar with Java, after all it is entry level. If you want to get a close to perfect score, you should do some practice tests. Even doing one would make a difference. Because one doesn't just find new information with practice tests, but also learns how to pace during the test which is key to getting a good score. You will also learn in what ways can they try to trick you with their questions. I didn't attempt any tests because I just wanted to get done with it as quickly as possible.