Ok I should be studying, but I'll give a quick explanation. I'll add in more later but feel free to ask questions.
The first spin done back in Dec 2009 was for location. 2nd years would submit their top choices for region and they were assigned accordingly. Note that 2012 students were allowed to trade/sell their assignments, but Dr. Kemper said she will discontinue it, presumably due to the mess it creates.
The next spin will decide which hospitals in the region that each student will rotate in. Several hospitals require selection by Midwestern's committee such as Phoenix Children's hospital, due to its high profile status. More on this later...
The final spin will occur sometime in Spring quarter, and this will decide the order of rotations (FM first or IM, etc.). After this is decided, your 3rd year is set.
Note that specific hospitals may be required for all students in a region if it is the only hospital in the area with ward based teaching. Also, if you choose a rural area, you gain an additional elective. Otherwise, you will have to live in one of the rural areas for that rotation, but they will provide you housing if you choose one of the areas in the powerpoint I posted way back.
Some extra info: rotations in CA are still on and LA is one of them (22 spots for 2012 I believe). The Ohio CORE is still there, but far from mandatory. I'll make this clear that there are plenty of spots within AZ and with more opening up in CA, people will get their top 3 choice location at the very least. That said, things change every year, so it might be a little different when you all step up. At least you can see what happens to us beforehand.
Let me know if you have any questions. I'll post more information as I recall it or when I get the powerpoint.