A couple of years ago, I remember Ars Technica ran an experiment for a day or so when they blocked end users who run Ad Blocker. (http://arstechnica.com/business/news/2010/03/why-ad-blocking...)

I recall it generated a lot of negative feedback, but at the same time, I'm surprised it hasn't been copied more widely: If you're the kind of person who's willing to use Ad Block on a site that's providing content financed solely by advertising, I would imagine you're also the kind of "customer" that at least some of those sites would prefer not to have.