The feature I've been using quite a bit, are the Wall and Scraps, as ways to quickly communicate with my friends. If you haven't used these, they're exactly what they sound like. You can leave messages for people to read on their "wall" or leave them a note (or "scrap".) The people can read these later at their convenience; the thing is so can everyone else....and they do. Features like Facebook's mini-feed make this easier to do, and so even more addictive. After all there's nothing more interesting than seeing what other people are up to.
Like leaving comments on someone's blog post, you're not just responding to person's comment or congratulating them, you're doing so loudly on record for the rest of the world to see: its not a private conversation, its a public toast/roast. I'm not sure what the right analogy is; if an email is like a private conversation between two people, a "scrap" or "writing on a wall" is like shouting to a person across a room, or writing in their scrapbook knowing its going to be passed around right after?
Anyway, what I was trying to get to is that the Observer effect seems to kick in, and the way people would communicate (tone, words, even if they would choose to communicate or not) changes. I've found myself scrapping people I'm not sure I would send an email too. I've had to catch myself from writing a little differently when sending an email to a list rather than just one person. A friend once told me he thought he was being "louder" and a little more obnoxious (than usual) on people's walls.
So maybe public scrutiny has a counter-intuitive (at least to me) effect. It seems to free people up to be bolder/louder rather than quiet them down.
But that's just my read so far. What's your take?