This might be the first good move Yahoo has made since Mayer took over. I can't think of a better example of a company that needs to shed worthless baggage and focus on high value propositions. And I am gobsmacked Yahoo has not at least made an attempt at a real social network. They have hundreds of millions of users, at the point they are in giving all their users an automatic account on Yahoo Social might be a dick…
Rather than building out a full-scale social network like Google+ they might be better served by aiming for something like Reddit, or HN. There's enough sociability and gamification to make it an engaging destination, but it's not confusingly trying to reproduce a Facebook. Of course maybe this kind of lightweight social network is what you meant in the first place.