There have been several articles the last week on this practice called "domain testing/tasting" (see for example this post by Bob Parsons, or an article by Loïc Damilaville in DNS News n° 96 [in French]). The Washington Post reports on the neighboring practices of "domain parking" and "typosquatting." Its article suggests there would not be any use of typoed trademarks without the possibility of displaying ads on the homepage, and that those who benefit the most of this practice are not typosquatters, but "Google Inc., which runs the largest ad network on the Internet".
In this article, it is written that Google "removes participating sites from its ad network if a trademark owner complains that those sites are confusingly similar -- even though close misspellings don't necessarily prove that a legal infringement has occurred." And so does Yahoo!: "Yahoo is strict about weeding out addresses that violate its guidelines, which prohibit celebrity names, typos of trademarks and references to illegal activity. Yahoo developed a software filter to identify domain names in its network that violate those rules so they can be removed.".
If a complaint of a trademark holder proves efficient, could it be a smooth and costless way of barring typosquatting? This could be the conclusion, but then one can wonder what happens with the infringing domain names: They are not removed, and can be used with another advertising program.