Facebook. That's really Twitter's major problem. Facebook used to be mostly friends chatting to family and friends, but nowadays it's the single biggest source of news links and the sort of viral spam that used to circulate on Twitter.

Twitter is still a faster and more reliable source of breaking news, but not that many people (apart from journalists) care about speed. And Facebook's threaded chat provides a much better way to discuss stories than Twitter.

In sum, for most people, Facebook's news feed is probably now a better Twitter than Twitter.