It is good to know that people are asking OCMs about how to approach the exam. Yury Velikanov provides his responses in How to prepare to Oracle Database 11g Certified Master Exam. I get similar questions myself.
I would only add that the exam is biased towards DBAs who work in an operational environment where you have to make decisions fast, and who are used to failing fast and picking themselves up quickly. The objective is to get a good enough solution quickly, not the perfect solution.
And remember, OEM is your salvation!