Are any of you doing a mock interview? I'm riding the fence as to whether it's worth the trouble of arranging one, etc. Do you think it really helps? If so, who's doing your mock?

I did one, and I think it can only help. I actually got nervous getting all dressed up, worrying about little details, like how I should wear my hair, even though I did the interview with a faculty member with whom I am completely comfortable. My mock interviewer was an OB/GYN. They recommended at our school that people who have been described as quiet (which I have been) do one, just to optimize the interviewing technique. I haven't had any real interviews yet, so I don't know how much it's going to help. Hopefully doing the mock interview has let me get some of my first interview jitters out of the way.