Minutes before beginning this piece, I twittered, “At home in Boston, writing about Twitter one more time.” Robert Scoble, author of the technology blog Scobleizer, wrote in Half Moon Bay, CA, “Life with Milan is definitely nuts. He wakes us up at 3 a.m. and we both look at each other and say ‘good thing he’s so damn cute.’” In San Francisco, Twitter cofounder Evan Williams wrote of cofounder Biz Stone, “Talking about Biz’s need to get better at twittering.” In Tokyo, someone named Shiru said, “I’m getting better at surfing. Okay, time to get back to work.”

On Pownce, Michael Owens, a 22-year-old graphic designer in Chicago, addressed himself sternly: “I need a way to force myself not to check social media and blogs and webcomics and all the other things that I get distracted by.” A short time later, he posted, “Holy Crap. The Care Bears Movie is on. That’s freaking awesome.” And over at Facebook, Ed Vaizey, an old college friend who is now a member of the British parliament, told his 233 other friends about his professional reading: “Just read Robin Harris’s biography of Talleyrand–superb; and Edward Pearce’s biography of Walpole, not so good, far too arch.”

These notes–terse, obscure, and endlessly self-referential–are all examples of a new phenomenon in social media called “microblogs”: short electronic posts, sent to friends or to a more general community, that deliver some information about the sender. Sending microblogs broadcasts, “I am here!” Reading microblogs satisfies the craving of many people to know the smallest details of the lives of people in whom they are interested. Already, new-media intellectuals have coined a term to describe the new social behavior they say microblogging encourages: they talk of “presence,” a shorthand for the idea that by using such tools, we can enjoy an “always on” virtual omnipresence.

As Kate Greene reports in her profile of Evan Williams, “What Is He Doing?”, ever since Twitter was named best blog at the Web Awards at the South by Southwest festival in March 2007, the number of people using the microblogging service has expanded swiftly. In March, Twitter had 100,000 members, according to Biz Stone; today, TwitDir.com, an independent Twitter directory, says there are almost 500,000 twitterers. But the most obvious signal of microblogging’s importance is the swelling number of Twitter peers or imitators. Recently, a Chinese blog counted around 100 “Twitter clones” in at least 12 countries. They all have cute, telegraphic names: Jaiku, Kyte, Plazes, Pownce, Yappd. Even Facebook has joined the trend. The smartest of the social networks now allows its users to send their friends short posts that describe their “status.”

Two services merit attention: Twitter, because it was the first and is the best known, and Pownce, because of its many features and the personality of its founder, Kevin Rose.

Twitterers use mobile phones, instant-messaging software, or Twitter’s own website to send and receive 140-character messages, called twitters or tweets. Tweets–which mostly answer Twitter’s prompt “What are you doing?”–are routed to individual friends, to networks of friends, or to everyone who registers with Twitter.

Most twitterers (or twits, as they are sometimes inevitably called) communicate with small networks of people they know, but the most loved have thousands of people who “follow” them (to use Twitter’s own jargon). Paul Terry Walhus, a developer from Austin, TX, had 2,421 friends as of late September. Robert Scoble, the technology blogger, had 5,880. John Edwards–the John Edwards–had 3,528.

But as Evan Williams told me, “Celebrity twitterers are really outliers, even though they get a lot of attention.” Williams believes that the service is best understood as a system that swiftly routes messages, composed on a variety of devices, to the people who have elected to receive them, in the media they prefer.

Twitter’s elegance lies in its extreme simplicity. Pownce is more complex. As with Twitter, one can send messages to friends or groups of friends as well as to the service’s general community. (Unlike Twitter’s messages, Pownce’s cannot be sent to mobile phones.) But you can also send your friends links, invitations to events, photos, pieces of music, or videos. In addition, you can finely discriminate which group or subgroup of friends will receive a particular post. It is this combination of private messaging and file sharing that makes Pownce seem so richly functional. Such features are more often found on fully formed social networks like Facebook; but Pownce retains much of the intimacy and directness of Twitter.

Pownce was cofounded by Kevin Rose, the cofounder and chief architect of the hugely popular news aggregation site Digg and the cofounder of Revision3, an online video production and hosting company that shoots ­Diggnation, a weekly news show that Rose cohosts. Much of the excitement that attended the launch of Pownce last June derived from Rose’s reputation for creating new-media companies that hypnotize their youthful audiences into cultish devotion. Pownce seemed especially cool because Rose decided that only those with invitations would be permitted to test the new site.

Most of the other microblogging services combine some features of both Twitter and Pownce. Jaiku, for instance, works with cell phones, as Twitter does, but like Pownce, it is more friendly to pictures and videos. A few have novel variations on the basic themes: Kyte grandly claims that it allows “anybody to create their own interactive TV channel on their Website, blog, social network, or mobile phone”–a kind of microblogging that bypasses the written medium altogether.

Critics of microblogging argue that the services are not sustainable businesses, because they merely float upon the speculative bubble of venture capital investment in Web 2.0 companies. More nastily, they complain that almost all microblog posts are stupefyingly banal.

Bruce Sterling, the journalist and science fiction writer (whose latest short story can be found on page 69), crisply articulated the latter argument when he wrote to me, “Using Twitter for literate communications is about as likely as firing up a CB radio and hearing some guy recite the Iliad.” The private-equity markets best express the first argument: while the micro­blogging sites could not exist without venture capital, the sums invested in them have been relatively small. (Twitter, for instance, reportedly received about $5 million from Union Square Ventures and other investors, a paltry figure for a company whose importance has been so hyperbolized by the media, bloggers, and its users.)

But it’s too soon to dismiss the microblogging services’ potential as businesses. Although all offer free registration, they could charge their customers and communications companies for premium functions. Pownce already charges its users for the ability to send large files. Perhaps the wireless carriers might pay the services to act as application providers for their customers; when mobile-­telephone users bought a plan, they could select Jaiku as an option. Another possible source of income could be advertising that is pertinent to a particular user; advertisers and the media buyers at advertising agencies, for all their disenchantment with print publications and broadcast media, will still spend good money for the type of effective, targeted advertising offered by Google AdWords and AdSense. Finally, the services could be used for direct marketing. Already, a few companies (including Twitter itself) are using microblogs to directly market themselves; since users don’t receive promotional posts unless they’ve chosen to receive them from the corporations they follow, the blasts are presumably welcomed.

My own experiments posting semiregularly on Twitter and Pownce produced mixed emotions. I quickly realized that decrying the banality of microblogs missed their very point. As Evan Williams puts it, “It’s understandable that you should look at someone’s twitter that you don’t know and wonder why it should be interesting.” But the only people who might be interested in my microblogs–apart from 15 obsessive Pontin followers on Twitter–were precisely those who would be entertained and comforted by their triviality: my family and close friends. For my part, I found that the ease with which I could communicate with those I love encouraged a blithe chattiness that particularly alarmed my aged parents. They hadn’t heard so much from me in years.

On the other hand, I strongly disliked the radical self-exposure of Twitter. I wasn’t sure it was good for my intimates to know so much about my smallest thoughts or movements, or healthy for me to tell them. A little secretiveness is a necessary lubricant in our social relations.

Jason Pontin is the editor in chief of Technology Review.