Twitter is a heady mixture of messaging, social networking, personal revelations of “microblogging” found on services like Jaiku, and something called “presence,” shorthand for the idea that people should enjoy an “always on” virtual omnipresence.

A Web site called Twittervision superimposes public tweets on a Google map. Every few seconds, a tweet appears and vanishes somewhere on the globe. It is an absorbing spectacle: a global vision of the human race’s quotidian thoughts and activities, or at least of that portion of the species who twitter.