The team is hoping to get some feedback on our new round-cornered ad units: [adsense.blogspot.com...]
We've heard from publishers that the square corners don't always complement the look or feel of their sites, so we're hoping this new option will allow for greater flexibility and blending on a wider variety of pages.
Just a clarification for everyone of what I've noticed, because lots of commenters on this thread are talking about borders:
If you use ad units without borders, but your ad unit has a different color than the background color of the page, you will still see rounded corners with this new feature.
So, although I acknowledge most users without borders on their ad units are blending and so will have the same background color and page color, if you're not, you can use rounded corners with or without borders.
And by the way, the non-ad part of the rounded corners is correctly transparent, thank you G engineers!