* Google Affiliate Network: As part of the integration of
DoubleClick, the DoubleClick Performics Affiliate Network will now
operate as the Google Affiliate Network for advertisers targeting
users located in the United States. Similar to the AdSense
Referrals program, the Google Affiliate Network enables publishers
to apply for advertiser programs and get paid based on
advertiser-defined actions instead of clicks or impressions. For
further details, please visit:
www.google.com/ads/affiliatenetwork.

* AdSense for content ads: If you have less than three AdSense
for content ad units on a page, you may wish to replace the
referral ad units with standard AFC ad units.

In Google’s email Monday, they suggested removing all referral code from sites prior to the last week in August. In addition, Google suggests saving account information for future reference as AdSense Referral code will no longer function after the last week in August 2008.

UPDATE: http://adsense.blogspot.com/2008/06/were-retiring-adsense-referrals.html