I've been trying to figure out how to explain Twitter to people, and the best analogy I've come up with is this:
Imagine that you're working in the same room as a bunch of interesting acquaintances. You're all sitting around a room, hanging out. If this were a real-life room, from time to time someone might catch your eye, and say, "Hey, I had a weird dream last night", or "I've really been worried about my grandmother all day." or whatever. Typical casual conversation about what's going on, nothing too in depth, just spontaneous chatting.
Now imagine that some of these people who are sitting next to you and chatting are famous writers, actors or rock stars. Imagine that others are Iranian dissidents. And imagine that instead of hanging out in your apartment, they're out in the world, doing various things (prepping for a rock show, writing a novel, hiding from volunteer Basij militia).
And there's Twitter. Amanda Palmer is getting to be a pretty big deal rock star, and I've been watching her flirt with (and eventually start dating) one of my favorite authors, Neil Gaiman. Wil Wheaton (the guy who was Wesley in Star Trek) often writes about how nervous he is during auditions, or how he's got writer's block. There's a spot of trouble in Iran just now, and @persiankitty (and lots of others) are posting updates about their experiences in real time.
Twitter feeds certainly aren't very deep or insightful, but they have an intimacy that is genuine. Because it allows for spur-of-the-moment composition, and because the medium is impermanent (it's extremely difficult to follow twitter feeds except in real time) it allows strangers to share a sort of "behind the scenes" confidence that is pretty unprecedented*. These aren't carefully crafted announcements or ghost-written publicity statements but, rather, spur of the moment thoughts. @persiankitty isn't making any big claims about what's happening in Iran on a macro level, just that she (he? they?) saw someone get shot, can hear sirens, &c. Palmer and Gaiman were just being very cute together*.
There's an immediacy that adds value to twitter messages, whether they're from protesters in Iran or actors in America. I'm tempted to say that I "feel like I'm their friend", but that's not actually true. I don't feel like I'm their friend but I have access to the easy, casual type of discussion with these people that has hitherto only been possible with people that I knew at least casually.
For me this is one-way access--for all that I care about the situation in Iran, there are few Iranians who care about the situation in Evanston. However, this isn't necessarily the case. I am allowed to send messages to anyone, and a lot of high profile folks regularly respond to messages via Twitter. Stephen Fry (a relatively famous actor in Englang, at least) "talks" to folks frequently, as does Warren Ellis and John Cleese. Trent Reznor seems to get into rather nasty fights with random fans (or, I suppose, anti-fans) over Twitter.
Even more interesting was the time Amanda Palmer started an all night party for people who (like her) were wasting time on the web on Friday night instead of partying. And took photos.
*Well, it's been possible to do this for years via bulletin boards and IRC, but that's a very self-selecting audience. Twitter is available to anyone with a cell phone or internet access.
*Yes, I hate that I'm even slightly invested in the romantic lives of two celebrities that I will never know, but they are awfully cute together.