europeforvisitors - 10:19 pm on Mar 21, 2007 (gmt 0)

Under CPC, the advertiser has already paid you for the click and now its their responsibility to convert it. CPA takes the risk away from the advertiser and puts it on the publisher.

Sure, in the same way that CPC takes risk away from the advertiser and puts it on the publisher (and the ad network). But higher risk = greater rewards for publishers who deliver quality traffic and leads.

FWIW, some publishers of "content sites" earn a lot more from affiliate partnerships than from AdSense. If you've got the right topic and audience, CPA can be very lucrative.