I like that one the best! It's like being back in "school". Makes you use your brain a little and teaches you to investigate. It will also probably help those who like to prepare their talks 1/2hr before the meeting.
i think it's gonna be a rough one to substitute for at the last minute. i've had school overseers approach me during the instruction talk to see if i could do a #4. that's no problem when it's coming right out of the reasoning or IT book. but with no material...*shudders*