I just wanted to jump in with a bit of information that might be of use to you guys. I was on the umich waitlist last year so I know a bit about how it works. First of all, it's broken into three tiers, as you know. I am almost positive that it is NOT broken into equal thirds. I was in the middle tier last year and I got in over the summer. Also, the way they seem to take people off the waitlist is that if an in-state female acceptee chooses NOT to accept her place at michigan, they will pull another in-state female from the waitlist.
The good news is that there tends to be quite a bit of waitlist movement. I'm not sure what percent of my class came in off the waitlist but I heard that something like 40% of the M2 class came in from the waitlist.
Hang in there! And if you REALLY want to go to Michigan, make sure they know that.
(There was a similar thread during last year's waitlist season so you might do a search for that if you're curious.)