This could have a negative impact on the earnings of Google Adsense publishers. A text link with an image on the left would attract more attention of the visitor and is more likely to be clicked than the one without an image. And premium advertisors might be paying less per click. So your Google.com Adsense CTR may go up but the EPC may fall.
Or, Google might be still testing this adsense feature and may eventually allow all adsense adwords users to use favicon in their ads. In that case, the skyscraper units will definitely catch the eye of the person viewing the webpage, which will be good for publishers as well as the advertisers who are using them to attract clicks.
DigitalPoint members have seen favicon icons even in LeaderBoard style. See some screenshots of Google Adsense ads embedded with icons here or here
Try the free Favicon Generator - Simply select a picture, logo or other graphic (of any size, resolution) for the "Source Image" and click "Generate FavIcon.ico"