Paying Per Action instead of Per Click in Google Adwords
successfulsoftware.net
A test comparing real world results of Cost Per Action (CPA) vs Cost Per Click (CPC) in Google Adwords.
successfulsoftware.net
One interesting thing to note is that Andy tracks conversions via purchases. I have always done it via downloads: contra "I think it is unsafe to assume the number of downloads correlates closely to the number of sales." it has been my experience that those numbers track each other like a pair of identical twins dancing salsa.
You can see my numbers here from waaaay back in 2007 here. They conclusion hasn't grossly changed in $10,000 I've spent on AdWords since that blog post.
http://www.kalzumeus.com/2007/11/10/conversion-optimizer-adw...
Possible conflict of interest note: Google did a case study with me about this product.
http://www.google.com/adwords/conversionoptimizer/bingocard....
I'm not sure from Andy's blog post whether he gets most of his traffic from AdWords on search or on the content network, although if I recall right it is search. I, somewhat surprisingly, do much better on the content network, although prior to using the Conversion Optimizer I thought it was a hive of scum and villainy. (I still think it is a hive of scum and villainy, come to think of it, but CO ensures that it isn't my pocket being picked and that is good enough for me.)