Use your Google or Facebook account to log in to any Yahoo services? Not much longer you don't: s0on, you'll need a Yahoo sign-in to access any of Yahoo's products.
It's one thing when MySpace decided to give up and give in to FaceBook, but Yahoo is...well...it's Yahoo. Saying you no longer need a Yahoo account, and can just use a Facebook or Google account to log in, is like walking out of the trenches with a white flag saying, "please be gentle with our assets." [AllThingsD]