Google will be phasing out the AdWords pay-per-action beta in the last week of August 2008, as announced on the Google AdWords Team blog. As an alternative to pay-per-action advertising, Google offers two products that allow you to manage your advertising on a CPA (cost-per-acquisition) basis: the Conversion Optimizer and the Google Affiliate Network (previously known as DoubleClick Performics Affiliate).
The Conversion Optimizer is an AdWords bidding feature that lets you specify a maximum CPA goal for ads on the Google search and content networks. It uses historical information about your campaign to automatically adjust your CPC bid for each auction to help you meet your CPA goal. In addition, the Conversion Optimizer is now supported in both the AdWords Editor and the AdWords API. You can learn more on the Conversion Optimizer homepage.