Their blog post indicates they're trying to go beyond that, to include social media content: "We want to experiment with and add value to the sources of inform

Their blog post indicates they're trying to go beyond that, to include social media content: "We want to experiment with and add value to the sources of information that are increasingly important, but difficult to surface and organize in most reader applications — like Twitter, Facebook, Tumblr, Reddit, LinkedIn, or Hacker News. We likely won’t get everything we want into v1, but we believe it’s worth exploring."