I do calls with client teams multiple times per week. Developers, ops, project managers, etc. I would peg the number at 5%. I say 5% because on one recent call with 20 people there was one person using a camera.

Additional of all the people I know - friends, family, parents, children, etc., only one of those people use the camera on their laptop. Some use facetime on their phone. But even for the mac users, it's a complete rarity.