One of the things I found really interesting about Twitter Trends is that they'll weight tweets or hashtags that appear across different clusters of people that aren't connected to each other on Twitter higher than a lot of activity that happens in a densely connected cluster of people.
You can imagine the opposite choice, where something that happens in a cluster of people really intensely, but isn't escaping — maybe that's exactly what should be revealed. Something like: You may not know anything about this, but somewhere, there's a lot of discussion about this, and you may want to know what that is. That's fulfills a very different public or journalistic thing. Yes, there are things that seem to be talked about on a wide basis, and we want to reflect those back, but we also want to say, over here in the world, in a place you don't have access to, there's something going on.