Think how google has sprinkled G+ across all their properties - I'm guessing Yahoo's next big announcement will be some kind of social layer bringing it all together. I would be most surprised if Yahoo did not already have 1000 monkeys coding away on some secret black ops social product that will launch in some form before the end of the year.
They've already said it: they want their homepage to be all about you. Think about what that means in this wider context, where they operate as an alternative way to discover content across all kinds of different verticals. They want to take over the space currently occupied by traditional media. For better or for worse, they're the most "human" of Silicon Valley's big web companies, and I think they might actually succeed.
I would argue though that social isn't about "you" - its about "them", your friends, your social network. Currently I'm not sure it its possible to "friend" or "circle" someone on any Yahoo page (excluding now tumblr), and "sharing" on Yahoo is just a series of exit links to every other social network. That must make Marissa mad.
