The biggest offender in my opinion is not the web, where you can install ad blockers and avoid certain websites, but television, where you're forced to sit through something before you can get to the content you're trying to watch.

I find it especially offensive on paid services like Hulu. I'm paying for the thing, just let me watch it!

It's also pretty bad for F2P mobile games, although the solution there is easy (play different games).

I actually don't mind advertisements in big cities or on billboards, sort of adds to the flashiness factor in some cases. Though if I lived in a more concentrated metro area I might feel differently.