Google launched their Pay Per Action ads a little over a year ago. Since then they have tried expanding it and marketing it to publishers and advertisers. We have extensive coverage of the Google Pay Per Action product at this site, if you want to check the history on it.
Today, I noticed a Google Groups thread that might imply that Google is having second thoughts of the product.
AdWordsPro Sarah, an official Google representative, responded to a question about the program:
Unfortunately, because the Pay Per Action pricing model is in beta, it is invitation only. At this time, invitations are no longer being extended while the product team figures out what direction the model will take in the future.
From this we learn:
(1) Google stopped sending out invitations for PPA. (2) Google is not sure what direction they want to take the PPA product in the future.
Was Google's Pay Per Action model a failure? Or was marketing it a failure?
Forum discussion at Google Groups.