Accurate figures are difficult to obtain, in part because prices are falling so quickly. Weak demand leads to widespread discounting, and banner ads often sell for a small fraction of the list price. It is quite possible that the falling price of advertising space stems not from weak demand, but from an abundance of supply. The Web is growing rapidly. The number of Web pages on which banners might appear, and the number of Web pages viewed, are ballooning daily.
Abundance drives down prices.
When banner ads first appeared, publishers charged about 4 cents per exposure. This would indeed be an economic revolution. Movie review sites would earn more than the movies they cover. It would be more lucrative to run a fan site about a television star or basketball player than to be an actor or an athlete. The number of viewers who click on banners has declined rapidly as well.