Wait until you see cost-per-lead and cost-per-sale. Web publishers that complained about advertisers wanting to pay for ads based on how many users clicked on them have a real challenge ahead as more and more advertisers adopt a direct marketing model for the Web. Agencies already are whispering about being paid on performance-so many leads or sales, so much payment-and they're starting to demand that sites do the same.
The cost per impression model will fade away over the next year as advertisers and their agencies demand more from publishers than mere eyeballs. They'll want the whole body, and the more creative promotions sites can drum up, the more dollars they'll see.