Re: ettiquette question
Once at a big seminar, I was in the second line and my sensei was in the front line. There ended up being an empty space in front, next to him. He turned and gestured for me to move up. Heh. I did, of course. I guess it's not cool to have an empty gap in the line.
I don't think it matters at big seminars; I just think the dans want to sit in front and the kyus are a little more "timid". I have sat in the front line many times since then.
I have never trained at a dojo that lined up according to rank, but if I ever do, I'll just be sure to ask.