Yahoo Publisher Network ads have undergone yet another branding transformation. First they appeared as "Ads by Yahoo". Then they changed in April to "Ads from Yahoo!"
Now, they have undergone yet another branding, this time following the quirkiness of the Google, but using "Ads by Y!" on their ad units
Still no word on when YPN will be launching in beta, but it shows they are still actively working on tweaking them before launch..