Ad blocking can become a real problem for the media industry (see article from The Economist, see also this WSJ article). Ironically, I dont think it'll really affect the big advertisiers (Google, Facebook, etc.). These firms can negotiate with Adblock tech firms to pay a toll for their ads to pass. Similarly, they might be able to force consumers to look at ads: e.g. Google can deny service if adblock is installed - will people say, no I am not using Google? Not clear. On the other hand, what might happen to small sites living of advertising is not clear. In other words, Adblock might lead to an even more concentrated ad market.