When I write articles, I try to minimize the number of ads in them in order to have better control over where the user clicks. If, for instance, a user clicks on an ad selling "knifes", he or she is unlikely to revisit the website and click on another ad or link on the website. With each successive ad, the control over where the user clicks becomes more chaotic.

The basic premise is the same as the one mentioned in Biz 2.0 magazine: If there are no ads on your site, you will not make money off of it. If there are too many ads on your site, nobody is going to click on them.

Daniel, thank you for posting this since before reading it, I did not have any factual data to back my claim :)