We covered this on the mobile ad side about two months ago, where Google is testing showing an "ad" label on the AdWords ad, as opposed to the standard format of a different colored background and sponsored label.
Google is now testing this ad label on the desktop results. I don't see them myself but Brian Ussery on Google+ and Rubén on Twitter sent me pictures.
Here is an image of the new format for desktop AdWords ads:
As you can see, the ads kind of blend better into the organic listings but at the same time, the hot gold ad label does make it stand out. I assume Google can make that gold yellow color more gray over time to make it blend better. ;-)
Ruben explains how to opt into this test on his new blog.
