Which is very interesting, because, in many cases you'll find people who are presenting to large groups, say, an auditorium full of people, or even just a conference room of willing attendees, in a situation in which the speaker is expected to speak at some length , and it is understood and to be expected that the audience will remain silent in order to receive the message, even in those cases, speakers will continue to use the your-turn, my-turn habits of speech, with the blank-filling um's and ah's and so on.
I listened to a guy from Toastmasters once, and at the start of the speech he said, "Will you please pull me up if I say 'um' or 'ah' at any point?" And he didn't, over the course of an hour or so. The trick, apparently, is to speak deliberately and know what you're going to say before you say it.
