Also note that the entire morning is mostly spent in Bartlett Theater, where you listen to numerous speakers talk about... whatever... then you watch a movie about COMP starring Noah Wiley, then you wander around campus with a guide, then you eat lunch, then you FINALLY sit around outside the faculty offices until your name is called to interview.
If you're the type that gets more and more nervous as time goes on, you may want to bring something to do, iPod, etc...
And lastly, my interview was in one of the faculty offices with table and such (good for hiding bouncy knees). I was not asked any ethics questions, and it was a very casual interview.
Good luck, don't sweat the interview!
