I don't know if this is old news. But it seems kind of sad how far the mighty have fallen. To let your users sign in with your (old) competitors buttons. Ouch!!!
You've been able to do this for Flickr for quite some time and I believe all Yahoo login pages use the same template.
It is a bit old, I remember seeing this in 2010, I believe.
It's weird to see how far Yahoo! have gone.