I assume it's usually like this:
-- later script checks to see if the first one fired; if not it pegs you as an ad blocker
I noticed one aggressively monetized blog a couple of years ago that apparently tried to withhold the content until ads could be verified to have loaded. Alas, if one of the many ad servers was slow, it choked their whole site so they had to give it up. Are there any other methods used?
The typical cure for an adblock blocker seems to be just a blanket exception for the site in the filter (i.e. total surrender), perhaps with ad-hoc site-specific re-blocking of some of of the ad networks they use. Is that a fair impression?