What I find interesting is that the whole idea turns around at this stage. It's no longer where you post your secret thoughts, just those that you don't want to make the effort of actually discussing with a person. Those that might possibly interest someone, but that aren't worth the time and effort of sitting down over a pint. Also, it's used as a kind of "as needed" newsletter, for those who want to keep up to date with your life, and occasionally as a communication tool to organise events etc.
With this in mind, it's really the things that you're not posting about that tell your friends what's on your mind. From a mathematical point of view, the difference between the set of "things your friends know are affecting you" (A) over "things you're posting about" (B) leaves a set of "things that you don't really want the world to know" (X).
Or A/B=X, in set theory notation.
Er, that's bit bit indecipherable for most, maybe. Basically I'm trying to say that if you know what's going on in someone's life, it's probably the parts of that which aren't being held up to the world that are maybe bothering them or that they feel aren't resolved.