Pretty formal. We have a protocol for everything we do on the mat. If I have something I want to say, I'm careful of the timing and considerate of the instructor's authority over the students.
Paul Huber Sensei is a very down-to-Earth guy, but being Aiki children of Kit Hathaway Sensei, we all consider we're representing her reputation among other Aikidoka and the public. So observing proper dojo etiquette is a matter of honoring her. She's outspoken, too. So that only counts for how we behave on the mat.