A Webmaster World thread speculates whether Adsense will become an obsolete business model with the introduction of Pay Per Action ads.
Some members think that it will remain the same:
The reason CPA won't replace CPC is simply because most publishers won't go for it. It's work to hand-select ads and hand-place them on the right pages, and for what? The CPA model is tilted in the advertiser's favor, so there's really no reward for the additional work required of the publisher.
Others disagree:
On the contrary: The rewards can be much greater with CPA than with CPC, if the publisher has traffic that converts. The real question isn't whether CPA works; it's whether there's a benefit to working through a network like Google or Commission Junction instead of dealing directly with the affiliate partners.
Additional discussion, including the impact of Pay Per Action on other affiliate networks, continues on WebmasterWorld and DigitalPoint Forums.