I have had both interivews this week (one for Lauder, and one for Wharton), and I dare say that the experience is very similar to the gruelling panel Selection Interview I had with the United Nations three years ago. Tough stuff!
In my case, both interviews were longer than 30 minutes, and the questions were very detailed, spot-on clarification promts. No "why MBA", no "why Wharton" routine for me! It seems that most questions were designed specifically for me.
The most helpful piece of advice I have ever received that is VERY relevant to the interview process is
to be yourself. It is a deceptively simple consept, isn't it?
It seems that for Wharton, your "self" alone is a very important factor in determining your fit.
On the personal side, I was so impressed with my interviewers' accomplishments; both of them have done some truly amazing things in their lives, and both seem to be an easy source of inspiration for people around. I definitely would be psyched to be in the same boat with them. Let's wait.