Unlike the traditional Google ads where publisher earnings are based on number of clicks or ad impressions, Adsense Referrals program will pay publishers when site visitor click on the referral ads and perform a specific action on advertiser's website which could be signing up for a trial account, purchasing a product, etc.
This is very similar to Firefox or Picasa referrals where Google was paying the publishers whenever a new visitor downloaded and installed any on these software. In the new Adsense Referrals, publishers are not limited to Firefox, Picasa or Google Pack.
You are free to select products to refer on your site - they can be based on keywords (like MP3 players) or you can select specific products from Google's Adwords inventory (like Apple iPod).
Google is providing all the regular Adsense formats for these affiliate ads which should make it easy for advertisers to integrated them in their existing site layouts thereby improving the performance.
The good part - Website owners have a greater say in the kind of ads that appear on their site instead of displaying ads suggested by Google.
The bad part - Adsense referrals beta test is currently available only to English-speaking publishers located in the United States. You will not receive payment for purchases made by visitors who are not based in the US.
Google Adsense Referrals Beta | Adsense Blog