@Jeff .. It is not about taking notes. I always take notes. I am talking of certain situations. An example: If I am just starting as a PhD student in US and I see my prospective advisor (and his collaborators) discussing about something I feel to be very interesting, I do not think I will be able to pick up all the "deep and subtle ideas" that come up during such discussions (being a beginner). And if I do not pickup what is deep and what is not, I might miss those important ideas and consequently not jot down. It is very important for me to understand those ideas.