I've been using the new view for at least a year now. Even back when it was beta.
I believe the Top Stories ticket might be new but the tabbed views and mail client look isn't new.
This is the look that Yahoo! tested for many months prior to the release of Safari 4.0. In beta, it did not work particularly well with Safari 3.0. However, it worked very well with Firefox and Safari 4.0. There may have been an imperceptible tweak a few weeks ago, but the basic look and feel have been around for quite a while. So, if you are waiting for Yahoo! to work out a problem that you are having, you may be waiting a while.Now that I closed and reopen Yahoo! Mail, it has changed to the old design. Then I did it again and to the new one. I'll give them a couple hours to work this put, only been 10 minutes old
This is the look that Yahoo! tested for many months prior to the release of Safari 4.0. In beta, it did not work particularly well with Safari 3.0. However, it worked very well with Firefox and Safari 4.0. There may have been an imperceptible tweak a few weeks ago, but the basic look and feel have been around for quite a while. So, if you are waiting for Yahoo! to work out a problem that you are having, you may be waiting a while.