Now that I'm back home and have had a chance to think back on my interview, I thought I'd share my thoughts on what worked and went well, and what didn't go so well for the benefit of posterity.
1. Visiting the school before the interview: Granted, I visited the day before the interview, but the experience was nonetheless valuable. I was able to pick out things I had seen or experienced during the visit and use them in the interview to add to the questions of why Chicago. Also, the students were all very enthusiastic about the school, and it's contagious, so it helped me be enthusiastic about the prospect of going to the school.
2. Preparing...a lot: You've heard the cliche practice makes perfect, well it holds true here also. While I wasn't perfect in my interview, my preparations were key. Not only did I expect most of the questions I was asked, and so knew the main points I wanted to make for each question, but knowing how hard I had prepared allowed me to go into the interview with confidence. I'd recommend using resources like accepted.com, clearadmit.com, or other applicants to get a sense of what the interview will be like, and prepare accordingly.
3. Relaxing: All of the students I spoke to said the key was just to relax and be yourself in the interview. What they're looking for in the interview is more personality focused - are you friendly and personable, can you express yourself well, are you the type of person they'd want to study with, etc. Part of what let me relax was the preparation I had done, but also by taking steps to relax beforehand. Each person will have their own way of relaxing, but I picked out specific songs on my iPod that I knew would keep me relaxed and focused, and listened to them the morning of my interview before leaving the hotel.
1. I wasn't as concise as I could have been: The first question I was asked was to describe my career progression to date, and why I was pursuing an MBA at Chicago. Looking back, I spent a bit too much time focusing on what I had done in my career (I have 6.5 years of work experience, with two very different jobs) and didn't get to the why MBA/why Chicago part quickly enough. My interviewer asked a few clarifying questions as I was explaining my career progression, but after I had spent about 4-5 minutes on my career, he asked again why MBA and why Chicago. Looking back I could have been more concise about my history and gotten to the why faster.
Overall I think I did well. Looking back, other than trimming down my first answer a bit, there's nothing I would have wished that it had gone differently. I also only mentioned 2 of the 3 points I had for why Chicago (I left off a bit about the culture there), but the interviewer asked a clarifying question about one of the first two points I made and the interview went on from there so I didn't want to go back at that point. I walked out confident that the interview had gone well (and if the interviewer wasn't impressed he hid it well), and am now settling back in for the 6 week or so wait until decisions are released.
Disclaimer: I am not an expert. I have only done 1 interview at this point, and while I think I did well I do not know if my interviewer would agree (although he was smiling and nodding as I answered - but having been on that side of the table several times I know it's possible to smile and nod while simultaneously thinking "wow this guy/woman is way out of their league"). So, take anything I say with the appropriate degree of skepticism.