Google has informed users of the Adsense Referral program that the program will be retired the last week of August.
Google's first attempt at affiliate marketing first appeared in 2006 and launched in March 2007. The CPA (cost per action) network never really took off in a big way, being offered to publishers as a bolt on to the more popular, and far easier to implement Adsense program.
The email sent to users advised that all referral code should be removed prior to the closure, that users should substitute referral units with Adsense units, and reports will be available until the end of August. Also being chopped as part of the announcement is the Google products referral program, so users will no longer be able to run CPA ads for Google products such as Picasa or even Firefox. The help page would indicate that referral payments for Google products may already be suspended.
Although not mentioned in the email (or even linked from the Adsense help page), the likely reason for the closure is the launch of Google Affiliate Network, the rebadged DoubleClick Performics. There could never be enough room in Google for competing affiliate networks, and with Performics offering a superior platform and product choice (not to mention the $3.1 billion paid for the whole of DoubleClick) it was always going to be the winner. In usual lazy Google buys a company then doesn't integrate it properly for years style, Google users have to apply for a separate account on the Google Affiliate Network, and despite the initial rebranding everything but the front page is still branded Performics. I've applied and I'll report back if I get in so I can do a one to one comparison of the two offerings.