Hey Kreno,
I interviewed at duke back in november and it is by far my top choice school. The interviews are laid back and not stressful at all. The interviewers have all the info on you and have read it beforehand. Mine had questions all ready to ask so they had obviously taken notes on my application. When I went there were about 6-8 of us, I can't remember completely. We got there a little before 10, plan on getting there earlier because it's hard as hell to find the admissions office in the underground maze. (I went to duke undergrad and I was lost). A little after 10 you all move to a conference room and get a talk from Dr. Brenda Armstrong, who explains the duke system in detail. She's very friendly and cool. Then you see a rather cheesy film on financial aid. After that I believe we had lunch with a couple med students in a little room, not in the cafeteria. The lunches are ordered from an outside restaurant and are pretty good. The med students are really friendly and will answer any questions you have. After that we all returned to the admissions office and waited for our interviewers to call us. There are only a few interviewers so they get to see most of the applicants there on that day. As far as alpha and beta, don't worry about it. Most people can't tell which is which, and they want it that way. So just be yourself and pretend there's no such thing as alpha and beta. If you try to guess and gear your answer one way, you'll probably screw up. I thought my first one was beta for sure, but after the second, I thought my first was alpha. They do have student interviewers too, and they have just as much say as the faculty ones. I thought mine went pretty well, both the interviewers were pretty laid back and although they were asking questions, it became conversational. Be careful of ethical questions though, they seem to like them. After the interviews, you are free to go. If you drove there and parked in the parking deck, ask to get your parking validated so you don't have to pay for it. That pretty much sums up how it went for me. It's an awesome school and I wrote them a letter of intent already. I also interviewed at upenn, harvard, and yale, but in my opinion Duke is king. Have fun at the interview and put in a good word for me. Let me know if you have any other questions.