Sorry for the late reply - I was traveling today.
The Columbia day starts earlier than many places I interviewed, and there's a considerable chance your interview might not be till the afternoon. They weirdly don't tell you ahead of time. Columbia has only 1 interview, which I found a little unusual. So you might arrive by 8 am and have nothing to do until 11:30, when the dean comes in and talks to you, if you have an afternoon interview. Kind of stinks, but most of the ~12 people interviewing on my day were morning interviews.
The university is amazing. The hospital facilites, the education building, the bustle of the area... loved it. The students all seemed very relaxed; one of my top criteria for a school is "students that look and talk like normal people." They all spoke highly of Columbia even when they were away from the office and didn't have to.
I had a morning interview, and I have to say I did not come away with the greatest impression. I don't know if that was me not connecting well or just a bad fit, but I felt like I never really got to anything meaningful during my 45-minute or so interview. The interviewer, a retired faculty member, knew my application and had jotted down some notes, but they were mostly superficial. After that kind of interview, I really don't expect to get admitted, to be honest.
The downsides, as I saw them, were the first-year dorm - it's kind of a hazing process, living in a run-down dormitory before you get to move to really nice digs second year and beyond - and the distance from Manhattan. I suppose the distance could be a double-edged sword, and the A train runs an express right to downtown, but I feel like I'd suffer from occasional NYC envy being stuck up in Washington Heights.
By far, the highlight of my interview day was the 35 minutes or so before lunch that the admissions dean, Dean Nicholas, spent with us. He pulled up a chair, we sat in a circle, and he just made all of us feel so at ease. We went around the circle and each of us introduced ourselves. He asked us to talk about some things that we did to relax - as he put it, "how we find our bliss." What was most impressive was that he had a detailed, hand-written chart with each applicant on it, and followed up everything each person said with a personal detail. For example, one person mentioned his love for classical music and the dean remarked about the difference between two classical composers. I'm a classical music *****, but it sounded pretty knowledgeable to me!
That was just such a nice touch to me. It made me feel like the people making the call on whether or not to admit me actually took the time to go through my application and knew me.
Columbia is certainly a top choice for me, bad interview notwithstanding. Sucks to have to wait till March!