I made a mistake with my application, in that I set up a new e-mail address and did not check it regularly as I wasn't expecting a reply for a few weeks. I missed an important e-mail saying that I had accidentally sent a photocopy of one of my certificates rather than the original. When I realised the mistake, I phoned up panicking, as they constantly emphasised how they would make 'no exceptions' for late applications, and mine was incomplete. Although they have this tough guy act, they extended the deadline for me after I explained the situation. The lesson learned was that JET uses a lot of big talk to scare you, and acts more inflexible than it actually is.
At the interview great emphasis was put on appearance, you have to dress very conservatively and formally to fit in with Japanese expectations. I was asked about whether my preferred locations really matter to me, how I could cope if I weren't place there. It is quite intimidating, you are placed on a chair in front of a panel of two people, rather far away from them. One interviewer was Japanese, the other British.