A WebmasterWorld thread has publishers claiming they are seeing a new form of AdSense ads.
The new ad format is a text ad that also displays a logo or image within the ad.
@netmeg sent me a screen shot of this in action:
There is a mix of reactions to this new ad format. Some like it, some don't. I suspect it has to do with which image Google is showing in the AdSense ad and how that looks on the site displaying the ad.
Forum discussion at WebmasterWorld.