pg strike me as a good speaker. Yes the "uhm" thing was a bit too much on the pycon video, but I think that is easy to get rid of with a little bit of training

"Sometimes I have to pause when I lose my train of thought."

A lot of people state this as a fault in their presentation skills, but is it really? It can be quite powerful and captivating with pauses in an ever streaming chain of talking, and I really don't think the audience mind.