Perhaps no American company is more of-the-moment than Twitter, the real-time messaging start-up that allows people to publish their current doings, readings, and ruminations, or ask questions of their Twitter community and get fast answers.

Jon Stewart mocked Twitter on "The Daily Show" last week, showing a congressman Twittering away on his phone during a recent speech by President Obama. Google's chief executive made dismissive comments about Twitter, while Business Week speculated that Google might buy the company for several hundred million dollars. And Facebook, which tried last year to buy Twitter for a reported $500 million, is rolling out a redesign of its website this week, in part to try to duplicate popular Twitter features.

And yet, despite the San Francisco company's growing reputation among the digerati as the next potential Google, YouTube, or Facebook, few American companies are less of-the-moment than Twitter: It is able to raise new funding from sources that aren't the federal government (more than $35 million last month), it has no announced plans to make money from its service, and two of its Boston-based investors don't seem to be exerting too much pressure on Twitter to bring in that first dollar of revenue.

"The priority is still growth and stability," says Bijan Sabet of Spark Capital, referring to increasing Twitter's population of about 5 million users, and making the service more reliable. As for a business model, Sabet says, "we're going to try a few things this year that we're excited about." His colleague Todd Dagres told me recently that "we're in no rush right now" for Twitter to start booking revenue.

Twitter is the latest in a series of Internet-fueled comets, a series of start-ups that have included the instant-messaging service ICQ, Web-based e-mail hosting service Hotmail, illegal music-sharing network Napster, social hub MySpace, and Skype, the free Internet calling system. Each start-up has attained incredible momentum based almost entirely on digital word-of-mouth. Many have been snapped up by larger companies before they were forced to figure out how to stand on their own two feet.

Some describe Twitter as a "micro-blogging" service - a way to transmit succinct messages to a group of friends that Twitter terms "followers." Others liken it to Facebook's status updates, where that site asks "What are you doing right now?" and lets your community see and comment on the answer.