Some years ago (2004) I participated in the excellent session organised at the IMA in Minneapolis by Peter May and John Baez. My impression was that everyone thought highly of the lectures (I may be biased as I did give some of them.)
One principal principle used was that even when the 'big name' who had done the original work was in the audience, it was rather someone who had worked with and used that work who gave the talks. (I.e someone who had had to learn the stuff!)
The lectures were timed within the fortnight so that on one topic perhaps four hours were planned (but perhaps 6 to 8 hours were available!) We were encouraged to say... "can we have a bit more background on such and such?" (I noted several very interesting reactions where someone was a supervisor of some of the students who were there. The supervisor suggested that someone might expand on a topic for the sake of the students. Several times I noted that (i) the students looked very pleased at this, and (ii) lots of other people also looked pleased!) There would be a call for volunteers to give the extra sessions. They might be full sessions or just in the bar in the evening with a few people around someone discussing the topic.
The bane of lecture course by experts may be that they plan for four hours(or whatever0 and have a very intense idea of what need to be said. They therefore force feed the audience.. and , continuing the metaphor, the audience find it hard to digest. I did not feel that that happened at all in that IMA workshop. (If Peter or John see this may once again say that it was very instructive, very useful and very enjoyable. Thank you again.)