For a couple of weeks, mack has occassionally seen AdSense ad units on Ranx.co.uk that are unbranded, without showing the “Ads by Goooooogle” or the “Advertise on this site” that normally displays in his ad units. He was able to grab a screenshot of it the last time he saw it show up:
These are appearing in both banner sized ad units as well as the large rectangle ad unit.
Back in the early days of AdSense, publishers had the ability to “hide” the Ads by Google branding on the ad units, and most people definitely saw a higher CTR when the branding was gone. The primary reason for this was very simply that the ad units weren’t branded as advertising, and people seemed to give them a second look. However, advertisers weren’t quite as happy about the situation, especially when publishers then tried to disguise these unbranded ad units as links within the webpage or article, hoping visitors would click them and not realize they were actually ads.
I know many publishers would welcome the ability to run ad units without the Google branding. Currently, only premium publishers can display their ad units without the Google reference. So it is interesting that this is something AdSense is testing once again, albiet on a very limited basis.