NYTimes has an article on Adblock Plus, an ad blocking plug-in for Firefox: "The larger importance of Adblock is its potential for extreme menace to the online-advertising business model."
A quote from the plug-in maker: "There is only one reliable way to make sure your ads aren’t blocked — make sure the users don’t want to block them." he wrote.
I took two screenshots of the article page in NYTimes.com, one before the Adblock was installed, the other one right after, on default settings. The white space that was used by the ads is collapsed in the ad-free version. Click image to zoom in.
One way to trick the program is not to use third-party ad networks whose addresses are blocked. I ran Adlab through the plug-in: the AdSense is predictably gone, the hardcoded Amazon books are still there.