A look into the future
The present situation is highly unstable. It can't be long before the majority of users are blocking ads. The advertisers, and the sites that depend on advertising revenue, aren't simply going to say "It was good while it lasted" and walk away.
The first change is likely to be a switch to serving ads from the same domain as the main content. It's a lot more fiddly than simply pulling ads from content networks direct to the client, but with computers, once a fiddly thing is solved, it stays solved. This will make ad blocking a lot less deterministic, especially if sites avoid always serving ads from distinctive paths.
If blocking still succeeds, the next step is likely to be the development of ways to embed ads as binary content in HTML pages. I'm not sure how feasible this is at the moment, though it's already possible to embed base-64 encoded images and fonts. If this happens it will be nearly impossible to selectively block content.