The shelf exam weights will vary by school, and even by rotation within each school. In general, they are worth a lot less than the subjective evaluation by the attending(s) and senior residents. Being liked helps, but in third year there are other factors at play -- you have to be a useful member of the team (residents will generally weigh in), and you often have to outshine other med students who are on the rotation with you. I've seen cases where the attending clearly liked a med student, but then based the grade largely on what the senior resident said about him. I've seen cases where the attendings and residents clearly liked both med students who were on a rotation at the same time, but liked one better and the difference was reflected in the final grade, despite the fact that the less impressive of the two probably would have gotten a higher grade if he had been on rotation with a different classmate. Then there's situations here attendings or senior residents change over mid rotation and suddenly all the goodwill you have built up goes out the window because the folks who end up grading you missed your brightest hours. Welcome to subjective evaluation. It's how the world works out of school, not just in medicine.