The basic mechanics of Twitter are remarkably simple. Users publish tweets — those 140-character messages — from a computer or mobile device. (The character limit allows tweets to be created and circulated via the SMS platform used by most mobile phones.) As a social network, Twitter revolves around the principle of followers. When you choose to follow another Twitter user, that user's tweets appear in reverse chronological order on your main Twitter page. If you follow 20 people, you'll see a mix of tweets scrolling down the page: breakfast-cereal updates, interesting new links, music recommendations, even musings on the future of education. Some celebrity Twitterers - most famously Ashton Kutcher - have crossed the million-follower mark, effectively giving them a broadcast-size audience. The average Twitter profile seems to be somewhere in the dozens: a collage of friends, colleagues and a handful of celebrities. The mix creates a media experience quite unlike anything that has come before it, strangely intimate and at the same time celebrity-obsessed.