While Yahoo and MSN battle for search volume with Google, a small pretender to the throne, Snap.com , may have a chance to push them all off of the top of the hill. All search engines look to PPC to fund the rest of their search activities.
Well if the CPA model Snap is pushing forward with under the able assistance of Bill Gross - the creator of PPC, contextual marketing and many other web marketing methods as the head of IdeaLabs and other ventures.
With all of the problems the engines are having with Click Fraud - the CPA model would eliminate nearly all of them. True it creates a situation where the search engines and their publishing partners become affiliates for the selling companies - but the early part of web economies involved a lot of affiliate models. The bid based model of PPC could be introduced and platforms developed that would take the strengths of both and move them into an even stronger evolved space.
Sooner or later this is a model that will be very successful - the engines that run with it early could be the new Google, Yahoo or MSN.....