Somebody on Chicago's applicants' discussion board got the hold letter, went to interview, ended up talking to Dean Ann Perry, and reported part of the discussion as follows:
"She indicated to me that applications were up 5% this year at UChicago, and that she has to be extra careful this year in sending out any offers of admission. I'm not sure how this will affect my chances, but she did say that they are rejecting a lot of people and the fact that I made it this far is a good sign."
More applications, less applicants. Waitlist season will be interesting...
EDIT: "less" should be "fewer"