In my experience, there is not one particular source that can possibly prepare you for the written boards and there wasn't any individual source that was particularly invaluable. The test was highly random and the questions ranged from the obvious to the ridiculous (no I don't know what the seventeenth least common complication of a vacuum delivery is and I don't know what the standard resistance of an xx french endotracheal tube is...exaggeration, yes, but not by much). I pretty much stuck to the Prologs, the Primary Care Precis, and Wall's review course material. I walked out of the test thinking that it could easily go either way, but was ecstatic when that letter saying "pass" arrived a couple of weeks later. As long as you were well prepared by your residency, I would not fret and just make sure you review the material ad naseum. For further assistance, talk to last years seniors from your program and get the scoop on what they did. Just remember to relax and get plenty of sleep the night before! Oh yeah, don't get sick and tell all your loved ones that they are forbidden from getting sick, suffering major trauma, or dying in the immediate weeks preceding the test. Once the test is over, they are allowed to do so at their leisure. Good luck.