I've been asked by a couple of people, "What is Twitter?"
What Twitter Should Wants To Be - A place to check updates of your favorite bands or artists, your friends and family. "Hey, I'm at Opal Divine's right now for happy hour! Who wants to come by?" "Our album is almost complete! We're playing tonight at 11pm at Beerland..." And so on.
What Twitter Actually Is - Let's say you have a friend who's a jagass that likes to send you a text message every time he does something. "I'm out of corn flakes!" SEND "Boy, the line at the grocery store sucks!" SEND "What pants should I wear to bowling tonight?" SEND
Now, imagine you have 50 friends who do the same thing...and you like it, because you're retarded.