Reports from DigitalPoint Forums and WebmasterWorld show proof that Google is testing out a scrolling ad feature with AdSense. Here are select images taken from forum uploads of how Google has implemented the feature, take notice of the small arrows on the corners of the ad.
As you can see in these four sample images, Google has added arrows up and down (or left and right). When you click those arrows, the ads scroll to different ads.
Google is constantly experimenting with different methods of enabling users to interact with the ads.
The overall reaction to this new ad format is positive, so far.