I brought up something in my last post about friend/follow relationships that I think deserves more attention than I gave it: the social graph -- as it is currently constructed at least, where all relationships are equal and mean the same thing -- is not the same thing as an interest graph. The implication is that using a standard unweighted relationship network to predict what content should show up in my activity stream will result in me seeing a lot of content that I'm not really interested in. That's inconvenient at best. As Hunter Walk so charmingly put it, "I like you, but not everything about you."
For example, if I follow Joe Shmoe because he tweets about the latest technologies, I'm not particularly interested in his other passion, emu farming. Joe's tweets about emus cloud up my stream with boring noise. I'm interested in Joe and a certain topic, but not necessarily just Joe. Facebook is a little better about this because it doesn't try to show you every single activity your friends undertake, but then it also has a lot more information about our own interests and interactions.
The solution to this problem is mostly algorithmic, but there is a sharing aspect too: if users have more control over who sees what they post, then they can post specifically to groups they know are interested in what they're saying. Behavioral norms can be just as important as technological solutions, and if you don't make an effort to change it, the default internet behavior seems to be to share everything everywhere.