That doesn't seem like his point. I think he is pointing out that digg changed too much and changed too much of the UX and people got fed up and moved to the ne

That doesn't seem like his point. I think he is pointing out that digg changed too much and changed too much of the UX and people got fed up and moved to the next best thing. I don't think he's saying Zuckerberg is worried about reddit, he's saying Zuckerberg is worried about being a fad or a blip. And he should be. More than one metric is indicating that Facebook usage per-user is diminishing, or at least peaking.