Google recently acquired the DoubleClick Performics Affiliate operations in March 2008 and hence terminating the Adsense Referrals program this August last week.
They have officially announced this and advised all the users to remove the referral code from their websites or alternatively sign up with their partner,DoubleClick.
However the rules are slightly changed, previously we were allowed 3 content ad units plus referral ad units on a single page, but now you can have only 3 ad units in total.
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.
If you currently use referral ads, either to promote Google products or offerings from AdWords advertisers, AdSense Referrals code will no longer display ads beginning the last week of August. We encourage you to take the following steps before the product is retired:
# Remove the referral code from your site(s): Please take a moment to remove all referral code from your sites before the last week of August, so you can continue to effectively monetize your ad space.
# Run and save all referrals reports on your desktop: Create and save all reports related to the referrals program on your desktop, so you continue to have access to your valuable campaign information.