No, you didn't push the wrong button and accidentally wipe out all
your formatting. And no one hacked into your code and played with
your Web page.
Google has redesigned its ad units.
The changes aren't radical but they do offer a couple of small
advantages.
First, the "Ads by Google" tag is now at the bottom of the unit
instead of at the top. That means that users no longer get a little
warning telling them that what they're about to see are ad links.
They see the links then they're told that they've been looking at
ads. That's a nice little change.
The other change is the removal of the borders between ads within a
unit.
That's not a great surprise. Turning off the borders was always the
first step in AdSense optimization. It seems as though Google has
seen so many of its advertisers turning off the borders -- and
earning more as a result -- that it has now removed the option of
having internal borders altogether.
But that also means that you can have an external border around the
ad unit without worrying about seeing lines between the ads. The
only time that I can imagine someone doing that is if they had a
very modular page with content placed in separate boxes. For the
most part, this change is just going to lower the chances of new
publishers accidentally putting up their ads with the worst form of
poor formatting.
One thing we can be sure of though is that Google tested this new
look before it came out -- and saw better clickthroughs as a
result. We should expect to see the same.