Yahoo is testing a new search interface. The new interface moves the Yahoo logo from the left side of the search box, all the way to the right side. It also adds a menu to the right that opens various new options from Yahoo. Finally, the search button is blue instead of purple.
The image on the top is the test and the image directly below is the one most searches see on Yahoo, this way you can see it side by side. You can also click to enlarge:
I am not too sure about moving that Yahoo! logo to the right? Maybe Verizon is trying to make room for their logo. A couple months ago, Yahoo tested a different UI for search as well.
Forum discussion at Twitter.