To Wit: Twittering

Then this San Francisco start-up challenges them to say their piece in 140 characters or less.

That limit, tighter than even a text message's 160-character cap, forces brevity and encourages frequency.

So do the usual ways to post an update: cellphone texting, IM services, or a box on Twitter's site that counts down as you near that limit.

You can opt to write only for friends, but Twitter co-founder Biz Stone e-mailed that "80-90" percent of users choose publicity.

Follow their example, and others can search for you and click a "follow" button to get your updates, or "tweets."

You can then converse bulletin-board-style, posting new tweets to answer one another. You can also swap private messages.

Your reward for successful solipsism: a public count of how many Twitterers follow your updates.

You can further express yourself by adding a portrait and background image and changing the colors of text on your page.

And you can publish your tweets on other sites -- many Facebook users include Twitter updates on their Facebook profile pages.

Market researchers say relatively few users have taken up this two-year-old service's offer, but their numbers are growing rapidly.

Twitter itself won't reveal user numbers, and conventional Web traffic estimates ignore its phone and IM users.