PrepCast is really good. If no PrepCast, I don't think I can pass PMP.
PrepCast's explaination and details description help to understand more about what PMBok saying.
Even I tried 7 times (7 x 240 mins = 1400 questions) of mock exam and I didn't pass either of them, I still feel good because everytime I review PrepCast's question, I learned more.
My suggestion:
1. Everytime you completed prepcast, read through all questions whatever it's correct or not. (200 questions took 4 hours to do, and extra 8 hours to read through all questions for each mock)
2. Spare some time do the "incorrect" questions (say 30 mins or 30 questions)
3. If you already completed once PrepCast, no need to do it again unless you have plenty of time. Try to understand more from PMBok, "why" more than "remember".
4. Lucky is important, but enough preparation to complete and review 240 questions is also important, during the exam if you feel the question is strange, just skip it (More than 30 questions I faced during real PMP exam)