It's a pretty good idea, and they've raised a lot of money. But there's a big problem here. It's a problem that's systemic to most of the Web 2.0 headspace these days, so I'm not surprised so few people are paying attention to it. Look at where the focus lies: "keep up-to-date"; "use your social network as a tool for discovering interesting information." Like your friends are only there to push cool stuff for you to look at. You don't really want to talk to them; you just want to subscribe to them. Real interaction is almost totally ignored, both in the pitch and the execution.