An important thing to keep in mind about doing the DM course is something you need to consider before you join a course - will you get to work with real people - not just other dm trainees/students simulating things? As has been gone over in the other posts - the baseline training/knowledge isn't especially difficult. And as in other posts, the instructors (hopefully more than one!) are extremely important in helping you acheive real dive master status. They need to be enthusiastic and respond to you...you might not want to do things exactly as they do, but it is good to see a variety of styles and to recognize that individual styles can still meet a wide variety of client/diver needs if done in a professional way. Good instructors will encourage you to find your own style, to always practice that rescue until you could do it in a coma and to always keep asking questions and practicing/learning.
You need to make sure you are getting experience with all sorts of divers, students, non-divers; make sure you are getting in water with them, on the boats/shore dive prep, dealing with logistics. As a DM you will be expected to be able to spot potential problems and deal with them, spot nervousness and overconfidence, offer appropriate help/advice/encouragement to others.
IMHO the only DM courses worth anything are those that get you working with people from the beginning and don't just tack it on at the end for a few dives or part of an Open Water Course.