To judge from the numbers in Google's quarterly earnings reports, advertisers aren't dissatisfied with the network or its pricing model.
These numbers might need to be revised if a court rules that Google must pay substantially more in damages for click fraud then they currently are willing to pay.
(Which isn't to say that Google might not offer CPA for advertisers who prefer that pricing method, just as it offers site-targeted CPM ads for advertisers who prefer traditional run-of-site CPM campaigns.)
Actually, I agree with this. I think customers deserve choices. But the mere existence of the CPA option seems to generate unease among some of you. Witness the people who say they don't want to allow CPA ads on their sites, want to leave AdSense in protest over the introduction of CPA, etc.