When I was visiting a couple of weeks ago, Brooke said that when they start looking to take people off the waitlist, especially once it starts to get later in the summer, they are looking for people they know will accept the offer. That is to say, the more in touch you stay with the admissions office, and if you are contacting them every couple of weeks or so to give an update or express your continued interest. Also, she said that if you are really wanting to get off the WL, and you have a way to get yourself to DC even at the last minute, you should tell them that. If a chance spot opens up, they will call you first because they know you will be able to make it.
Also, she said that they couldnt say for sure when they would go to the WL, but that they would. And that it could start as soon as "in two weeks," which would be this week.
Maybe none of this is new or helpful, but now that I've typed it, I'm clicking post. haha.