hope the interviews are going nicely.
Like Soulsensei, I'm also a first year JET. I haven't been checking on the forums very often, but if you have any last minute questions, PM me and I"ll try to answer before your interview.
And as he mentioned, READ UP on your SOP. You will very possibly get questioned on it.
Those of you with teaching experience should also expect at least one question about the classroom. It can include your past experiences or how you may deal with hypothetical issues. This can include classroom management methods, staff interaction in and out of the classroom and other details. If you have to, pause for a second to consider your answer.
I found my interviewers, a Japanese staff member of the consulate and an American (ex-JET presumably), to be somewhat cordial but distant. Most of the questions were posed by the American, with only one or two questions from the Japanese staff member.
I can't remember all of my questions, but several revolved around classroom management and prior classroom experiences. I was also questioned on my SOP as I had mentioned that one of the reasons for embarking on JET was its stellar reputation. The American looked rather dubious when he read that and asked me to elaborate. My answer was about how JET is one of the largest scale exchange programs that has been ongoing for more than two decades. I was rather worried that I had flubbed the question, but he seemed satisfied.
In addition, I'd like to point out that while JET has a great reputation internationally, its domestic reputation is rather spotty.
Don't be worried if you're a fresh graduate, lack teaching experience or a basic command of Japanese. While my batch had a large proportion of educators, we also had a number of fresh graduates, people without classroom teaching experience and Japanese manglers. I belonged to the third group. In all honesty, I still do.