When Google's Adsense Referral Opportunities went public, there were only a handful of sites that didn't rush to drop referral code on their sites to promote Google AdWords, AdSense and Firefox with Google toolbar. But Google has recently expanded well beyond simply allowing affiliates to promote their own services directly.

Those closely following the Web business industry got a peek behind the wizards curtain when Google announced their plan to test out Pay Per Action (PPC) advertising back in March. I commented then that Google's PPA model would change Web advertising, and with the recent announcement that the broadening of the AdSense referral opportunities just started and would include offers from third-party vendors (in categories like Travel, Gaming, Shopping, etc.), one of the last pieces of the puzzle has been set in motion.

The Google Referrals program now allows publishers to choose specific products or groups of products to advertise on a site which matches their content. Publishers are able to choose up to 15 products (or specific ads) to rotate in the referral unit and choose categories and keywords to ensure publishers get new ads as they become available.

While publishers will only receive earning when a visitors to a website clicks on of the referral ads and performs an action defined by the advertiser (complete a sale for example), they will not be compensated for clicks on those ads. But with referral payouts frequently surpassing $20.00 (VistaPrint for example) and higher end services paying out $92.00 per referral (DISH Network) there should be no shortage of publisher willing to participate.

Advertisers wanting to get in on the Pay Per Action advertising at Google may have to wait a while. While they have expanded the test, it may take a while for the opportunity to trickle down to small and medium-sized businesses advertising on the 'Net.