Not really what you asked for, but I guess it's related:
College admissions dance gets longer, more complicated | csmonitor.com
Here's the relevant portion
"Aiming for about 1,400 students in its class, Carnegie Mellon enrolls 1,500, expecting that some who send in deposits will nonetheless jump to another school. Out of about 22,000 who applied this year, 3,000 were offered spots on a waiting list. By May 1, usually only 10 percent want to stay on the list, which would have meant 300. But Mr. Steidel says he was "a little overwhelmed" to find that by mid-April, it was 450 and counting."
No idea how many of the 450 belong to the 'priority waitlist' though
Does a higher than normal waitlist acceptance rate imply higher yield this year as well? If so, that doesn't bode well for those waitlisted (including me >.<)