Probably a lot.
We all do, and in normal conversation, they easily slip by unnoticed. But when you’re on a stage and all eyes are on you, two things happen:
1. You react to your nervousness and insecurity by saying or emphasizing things you normally wouldn’t.
I’ve retrained myself, but I used to say “Right?” at the end of practically every sentence. I felt I had to grovel for validation, I guess. After I watched myself on video, I killed all but the most occasional use of the word.
I’ve heard a few speakers say “Yes or no?” at the ends of their sentences. Again, I guess they want agreement or validation, but they really annoy the heck out of their audiences.
2. The audience is more aware of your little quirks and expressions because you’re the only one talking.
When I was on a webinar the other day, the speaker kept saying, “So, very quickly…” before he moved on to his next point. Why? Did he want to give the illusion he was going through his webinar faster because he said he was moving quickly?