Free! Why $0.00 Is the Future of Business
An excellent article about how digital technology allowed whole industries to evolve around providing their content and services for zero cost to the user. The sidebar features are also quite potentially useful.
I recommend reading all of the above. I am singling out that comment because it seems like an important distinction to make between free and no-cost. It quite reminds of the distinction we make between "free as in freedom" software and "zero cost" software.
When a site offers content at zero cost to the user yet shows advertisements, loading and viewing those advertisements becomes a sort of a burden to the visitor that he has to be willing to "pay" to benefit from the content of the site. When this burden is too high to pay (a site has too many or too intrusive ads) the visitor will leave and the site's business will suffer in turn.