There are screen captures of Google AdWords Pay Per Action at Flickr. The screenshots have been made public by webkidsan.
The PPA service enables advertisers to pay a pre-determined amount only when a pre-determined action is completed. Thus it differs from PPC as the payments will not be for clicks only. The service is undergoing beta testing for both AdSense and AdWords. For more details visit http://services.google.com/payperaction/
However, the screenshot reveals that the different actions are sale action, lead action and a purchase/sale action which seems to have been deleted. Webkidsan informs in a comment at SEO Roundtable that separate actions can be defined. Image ads will also be tried, not just text ads. Another new addition is going to be text link ads.