See here to see how the waitlist process works after May 1 when applicants given initial offers have to respond w/their decision:
http://talk.qa.collegeconfidential.com/discussion/comment/19656464#Comment_19656464
I think it varies year to year w/regards to the waitlist as it’s hard to predict how many in each applicant pool will decline the offer and for really good reasons (other Bachelor/MD programs, higher tier 4 year undergraduate institutions, the cost of the program w/o much scholarship/grant support or at least not enough to make a huge dent since you pay School of Medicine rate tuition from Day 1 of this program).
I think the calculation is also different for people who are out-of-state, as students pay a ridiculous amount of tuition for the program, so it may not necessarily be worth it even if you were to save 2 years.