I had the interview a couple weeks ago. It was really nice! You have one interview with a faculty member who had only seen your personal statement and one with a student interviewer that knows nothing about you who just asks you stuff from a list of questions. Both were really easy and conversational though I liked the faculty interview better, seems more laid back. Then you have a 15 min kinda interview with someone from the admissions committee, also really laid back. Good luck!
Oh and I didn't stay with a host at Pitt b/c I have family there, but I did the student host thing at other colleges and I thought it was great. I would think Pitt would be the same.