Read papers of my (PhD) interviewers, reviewed my research, practiced answering typical questions
What impressed you positively?
Everyone's willingness to share information.
What impressed you negatively?
Everyone's willingness to swear freely in conversation.
What did you wish you had known ahead of time?
No major surprises
What are your general comments?
I had seven interviews, four with researchers, two with administration, and one with a student. All asked specific questions, but many quickly digressed to "let me tell you about my research/program." They were all essentially conversational once I had found a point of commonality with the person. The only "difficult" interview was with one PhD who actually expected me to demonstrate my thinking ability; I worked hard to answer his questions, but I also really enjoyed the challenge and seemed to satisfy him by being upfront, honest, and unflinching.