There was an internet marketing manager on a podcast I listened to once that said the number of people using adblockers on the internet is essentially negligible, it's in the millions but a small percentage of all users (<5% if I recall).

edit: the Podcast was Talking Machines (about machine learning) http://www.thetalkingmachines.com/

This[1] is from a year ago, before ad-blocking became widely available on mobile, and they're still looking at hundreds of millions of users using adblockers.

I don't know how reputable PageFair is, but they estimate more than 20% of smartphone users are adblocking now[2].

[1] http://bits.blogs.nytimes.com/2015/08/10/study-of-ad-blockin...

[2] https://pagefair.com/blog/2016/mobile-adblocking-report/

That sounds like a very high number. At least anecdotally, I'm not aware of anyone in my circle of influence who uses a mobile ad blocker. My suspicion would be that less people use mobile ad blockers than on a browser.

I always wondered what would happen if say MS and Apple decided to just block ads by default on systems with their OSs.

IE has a built-in ad blocker for years.