I just called, upper third waitlist. I asked her about the waitlist and she gave me a pretty clear answer, parts of which have already been mentioned in this thread:
They take people from the waitlist based on gender and state of residence. For instance, if a male OOS applicant withdraws, a male OOS applicant from the waitlist gets an acceptance to replace him. Same thing applies for each comination of male/female and IS/OOS.
They DO take from the upper third of the waitlist first, but not everyone from the upper third will get accepted before people from the middle third start to get accepted due to the male/female/IS/OOS thing. For example, if a female IS withdraws but there are no female IS students left on the upper third waitlist, they will take a female IS from the middle third even if there are female OOS or male IS/OOS applicants left in the upper third.