My bf is a 2nd year there, so I can shed a little light on this. There's basically a lottery system where people get assigned numbers and can then choose the order of when and where the electives are from set tracks. Later, people can exchange spots/tracks with others. He says it's fairly complicated, but fair. Keep in mind that there are four sites - RWJ, St.Peter's, Princeton, and the Jersey Shore, where you can rotate, so how many rotations are available in each place varies.