I have never used it.
Now I am not usually super excited to see adds and if it is a site that I visit regularly and it has the option to pay to remove them then I usually will. Otherwise I really don't mind seeing them.
If I am not able to sit through a 30 second or so ad for the content I want to see then it probably wasn't worth it in the first place.
Frankly I was really hoping YouTube's paid channel thing was just an option to remove ads from selected channels and not separate channels entirely. However given no such option I really don't mind watching/seeing ads especially when I know it will support the creators of the content I am about to watch.