I was highly amused to have my advisor pass me a note during a meeting yesterday. It required a bit of acrobatics, and some assistance from an intermediary, since we weren't sitting that near each other. I accepted the note with some flashbacks to grade school, when such blatant note passing would have resulted in extreme teacher displeasure.
In this case, the professor started it, and the post-doc giving the talk wasn't about to call her on it. In fact, the note was extremely helpful - I knew the presentation should related to my research somehow, but it wasn't obvious, and her note explained it. And just to make it vastly entertaining, it was written on the back of her lunch receipt. I may just keep that for posterity.
Besides, NPR said just this morning that doodling can be useful during boring meetings. Note passing is a step up; maybe it's even more helpful.