A new way to pay. Pay-Per-Action

Google has recently announced the worldwide expansion of its pay-per-action advertising beta.
Pay-per-action is a new pricing model that allows advertisers to pay only when a pre-defined action is completed on their site, such as when a user makes a purchase, signs up for a newsletter, or completes any other clearly defined action. Since the initial launch of the pay-per-action advertising beta in March 2007, many advertisers who have used the new pricing model are pleased with the opportunity to have more ways to promote their products and services online.
Pay-per-action ads are only shown on publisher sites in the Google content network, also known as Google AdSense™ for content sites.