Got this email this morning no doubt others have had it to:

Hello,

Thank you for participating in the AdSense Referrals programme. We
will be retiring the AdSense Referrals programme during the last
week of August. After that time, AdSense Referrals code will no
longer display ads.

If you currently use referrals, either to promote Google products
or offerings from AdWords advertisers, we encourage that you take
the following steps before the product is retired:

* Remove all 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 that you can continue to effectively monetise
your ad space.
* Replace your referral ads with AdSense for content ads: If
you have less than three AdSense for content ad units on a page,
we recommend replacing referral ad units with standard AFC ad
units. This will minimise the risk of decreased AdSense earnings
when the Referrals programme is retired.
* Run and save all referrals reports to your desktop: All
Referrals reports will no longer be available at the end of
October.

We appreciate your patience during this transition. If you have
additional questions, please visit http://www.google.com/adsense/support/bin/topic.py?topic=14882.
Thank you for your support of AdSense Referrals.

Yours sincerely,

The Google AdSense Team

Further investigation brings about this:

What happened to referrals?

During the last week of August, the AdSense referrals feature will be retired for both AdWords advertiser products and Google products. After careful consideration, we believe that we can best serve our advertisers and publishers through two alternative offerings, AdSense for content and DoubleClick Performics Affiliate.

Beginning in late August, any remaining referral ads on your site will no longer work, and will appear as blank space on your website. In order to prevent a decrease in your AdSense earnings, we strongly encourage you to replace all referral ad code on your sites with AdSense for content ad code prior to the last week of August. You can get this ad code by signing in to your AdSense account, selecting the AdSense Setup tab, and choosing AdSense for content as the product.

If you'd prefer to manually select the ads that appear on your website in the future, we encourage you to check out DoubleClick Performics Affiliate.

At first glance it seems like the most obvious reason is googles acquisition of this new company, Double Click Performics and their desire to push users through this new company rather than their old referalls, although (having only had a quick look) I can't really see what the benefits are of this new company in comparison, it all seems like coperate jargon to me, rather than something usful to Joe Bloggs with a Blog.

But yeah, anyone else got any thoughts on this? Maybe a little peeved at losing that revenue or pleased at the prospect of a better oppurtinity through this new company?