I interviewed at MCW on 9/19 during the early decision interviews.
First things first, RELAX!!!
I found my interview to be VERY relaxed, in fact my interviews were both like having a chat with someone I just met. Not very much like a traditional "question and answer" interview.
I posted my comments on the SDN interview feedback page.
The most stress I had was caused by me just being a neurotic idiot, not by anything the school or interviewers did.
That said, when I went, there were only nine of us. I overheard the director of admissions saying that the next few interview sessions were full, with 65 people in them.
Anyway, I left the interview feeling very positive.
You will get your letter within two weeks. Mine came the following Saturday. I know this not just from my own experience, but from talking with many students of the school.
If you have any more questions, PM me or email me (address posted on my blog, linked below). I'd be happy to help.
Good luck in your interview!!!