I was talking about Twitter to a friend recently, and I think one of the points I was trying to make was this: when you are talking to people about what you think, it's easy to bullshit (as in when you IM, especially with people who aren't your close friends).
When you are relating to others in a big social group, it can be superficial, and kind of "gossipy" (as in Facebook's News Feeds, for instance). These modes of communication suggest a much greater degree of authenticity and candid expression than what they actually offer. At the end of the day, however, when we talk about what we are thinking, and when ego gets in the way, we all tend to bullshit a bit. Saying something can never reveal as much as doing something; this is something that is becoming increasingly clear in today's media.
The subtle genius of Twitter is that answering the simple question "what am I doing right now" is both incredibly mundane, yet much more revealing about who we really are than what we might say about ourselves. It's a very direct and personal manifestation of the "do, don't say" mantra that is at the heart of new marketing and the post-communication world we live in.
Just to be clear: I don't really pretend to know what Twitter might mean, in the long run. All I'm commenting on is the cool way in which a picture emerges of what a person is about from the things they DO, rather than what they might say about themselves. For this reason, it seems to go quite nicely with a lot of the things regarding transparency and authenticity that characterize what communication is about these days. And it is also a great example of how simple technology- messages are easily sent from a mobile, for instance- can unlock a new, simple, yet powerful mode of communication.