I've noticed off and on for the past couple months that sporadically my ads format changed, at least in regards to the Ads By Google part. It would change from normal text, the same as the ad itself only a different size, to Google's own stylized logo.

As of this afternoon the ads on all of my sites have been showing the stylized Ads by Google logo. This has been apparent for me on every refresh for all my 468x60, Leader Board, and Sky Scrapers which were not set for image only.

For now I like it, we'll see how it affects my CTR.