okay, first of all, let me just say that this looks like a nice forum. I'm sorry I didn't find it earlier.
Like a lot of people (I guess), I'm waitlisted at a few places and am obsessed with it (particularly with my first-choice school.) I haven't been accepted anywhere and don't relish the thought of waiting until August to find out. (However, I know this is possible.)
So I've been doing some exploring. Check out
http://prehealth.uchicago.edu/HPA-handbook/hpa14.html for the AAMC Recommendations. Wiggy- the policy (and keep in mind that it's only a recommendation) is that by March 15th, every school should have issued a number of straight acceptances at least equal to the number of seats in the entering class. This means that, if you applied late to a rolling-admissions school, you have a pretty slim chance of getting an acceptance letter before the summer.
But try not to stress out too much (easily said, I know), because I would estimate (from figures I heard when interviewing) that every school accepts anywhere from 80-120 students (with the exact figure depending more on the class size than anything else) more than the eventual class size. Not all these are pulled from the waitlist, of course. But still. Don't lose hope, because if you do, then I have to, too!
Oh, and "alternate list" and "wait list" are the same thing, but not every school means the same thing by either of those terms. In a lot of ways, the AAMC gives the impression that these schools are all the same--but they're not. They have different procedures and different priorities and different evolutionary pathways. (This is a good thing. (I hope.))
dugan