One of the leading issues that I hear from people who do not use and have not tried to use Twitter is, “What the hell is it good for?” This complaint is typically followed by a derogatory comment like, “Why should I care what Ashton Kutcher had for breakfast?”
I often have trouble explaining Twitter to a newbie, because the flexibility of the platform is pretty extreme. You can do things as simple and (relatively) useless as pushing out a stream of consciousness with your daily minutiae, or you can do the sort of thing that Tom Caswell started at Utah State University last year.
TwHistory uses the Twitter service to “re-enact” historical events by tweeting in the voices of key figures who were involved. They’ve covered Gettysburg, the Cuban Missile Crisis, plans are in the work for the sailing (and sinking) of the Titanic, and they link out to others.
From now on, when I am introducing someone new to Twitter, I’ll still try to generalize and explain the basic purpose; but I’m going to mention this, too.