This is a common habit for PG. I've seen him speak in person 2-3 times and watched a handful of videos of him, and each time I noticed the amount that he said "um". Obviously the content is valuable and worth listening to, but it is naive to say that these sort of distractions by any speaker are worth overlooking.

Unfortunately, these are distractions from the content, which is what matters. Simple exercises could could help fix the habit with only a few hours of practice.

A trick that helped me in college was to say "uh" or "um" every other word while practicing a speech. This mental trick causes you to be hyper-aware of the habit, thus helping you to subconsciously stop inserting the words into speech. Try it out sometime.