I think I saw somewhere in this forum that Columbia wasn't waitlisting this year, but I just wanted to say that the DGS confirmed they are. I was urged to make an informed decision, but also notify them as soon as possible if I decided on another school, because they had many candidates they would have easily accepted in other years/were eager to have (he said applications increased exponentialy this year!). In my case, I was told it came down to fit: I used some Columbia faculty heavily in my thesis, I'm interested in studying elements of the Harlem renaissance so it was site-specific (I stressed this in my SOP), and a lot of different potential advisors, rather than one or two people, could contribute to my research.
Just wanted to put that out there for anyone stressed--I would not take anything personally this year.