I have just passed the OCPJP 6 exam this afternoon with a score of 86%. I have decided to take the exam on Java 6 instead of Java 7 because I develop with this version at work and in every cases I plan to take the exam upgrade on Java 8 when it will be released because of the important features (like lambda expressions) of this future version.
Thanks to the coderanch community where I found the best way to prepare the exam. I have bought K&B 6 book which is a very good one. I was very surprised of my first scores (< 50 %!!!). I simply read the book again and my score became better. I complete my preparation with some free mock exams picked on the forum. As already said on the forum, I confirm that the questions of the book are harder than the exam questions so you can take it without a very high score. At the beginning, I have also read the chapter on serialization because it is interessant but don't forget to check the objectives which are not anymore on the exam on the Oracle website.
The K&B book recommands to mark the hardest questions and only answer the easiest first. However, I didn't do that. I read each question very carrefully even if they look easy because there is a lot of traps. When you have completed the exam, you must wait about 30 minutes to have the result sent by e-mail. I have read that the result was immediately delivered before. On the score report, you can see all objectives where questions have been answered incorrectly. By remembering the questions where I had some doubts, I think the most of my bad responses are related to the fact that English is not my native language. I loose also some points with questions on the date/text/locale APIs which are the most annoying parts of the exam because of the various methods you have to remember.