The AdSense Referrals Beta, which Google launched at the end of March 2007 and open to U.S publishers only, is now available to all AdSense publishers. It is now known as Referrals 2.0
AdSense Referrals is CPA ads. Unlike CPC ads, you only get paid by CPA ads after your visitors satisfy certain actions required by the advertisers. It is harder but higher revenue.
