AdSense have just announced in emails to publishers that they have pulled the plug on the ‘Onsite Advertiser Sign-Up’ feature that used to appear on some ad units (links that used to read ‘Advertise on this site’.
The removal of this feature is a result of it’s poor performance and will soon be completely phased out.
I think it’s a good move – one less link on the ad units for people to click instead of an ad. Hopefully most advertisers are savvy enough to know how to target sites using AdWords.
Sounds like the team at AdSense are doing an overhaul of the system at the moment with changes to their reports hinted at (and announced), moves from site targeting to placement targeting and the changes to clickable zones in ad units all in the last 2-3 weeks.