I'm a little late on this thread, but I will suggest one theme that's only been lightly covered here:

On an interview, it's your opportunity to interview the company right back. You're about to get your reputation co-mingled with theirs, and you're about to deal with them most of your waking hours most of the days! I'm really a big believer in that.

You're bringing as much to the table in talent as they are in cashish, so you should be the interviewer every bit as much as they are.