They usually cease interviewing around late April. The waitlist phenomena is dependent upon the applicant pool of that year. For example in the 2007 class (my class), we had a lot of movement from the waitlist, while last year's class did not have any at all (in fact the class was too large because no one dropped...). The waitlist is dependent upon the students that were accepted to see if they go to another school or not. They usually overshoot acceptances to make up for the drops, meaning that if you are on the waitlist, you are also behind some people that are statistically expected to drop. They expect a class of approx. 200-205 students +/- 5-10 depending on the drops. If you are on the top of the wait list like in the top five, then you have a moderately good shot at acceptance. The reason that people can get accepted so late in the year is due to those drops. I know two-three students in my class who got accepted only 1-2 weeks before school.
