Although Facebook took a few years to grow from adolescent chat site to its current broader appeal (no doubt to the displeasure of the college kids), Twitter has leapt into the public consciousness in a much shorter time.

About a year ago, the free micro-blogging service was getting about 100 mentions in all media in a given week. Maybe a dozen or so of those were in major newspapers and magazines. Last week, for comparison, Twitter was mentioned more than 1,000 times in all media and more than 200 times in major publications.

Twitter users are overwhelmingly young, but unlike most of the other social networks, Twitter is not dominated by the youngest of young adults, according to a new survey by the Pew Internet & American Life Project.

The median age of a Twitter user is 31, compared with 27 for MySpace and 26 for Facebook. (The business-networking tool LinkedIn skews much more heavily to an older audience. Median age: 40.7.)

“What we don’t see with Twitter … that we do see in (social network service) use, is a decline in use in the 25-to-34 age group,” Amanda Lenhart, a senior research specialist for Pew in Washington, wrote in an e-mail. “I think that’s one of the more surprising findings.”

Twitter epitomizes how new media improve as more people find new and different ways to use them. The earliest Twitter users, in 2006, basically shot each other tweets about what they were up to at the moment. Knowing that a friend was “eating a sandwich” or “out shopping” might be useful to know now and then, but Twitter wouldn’t have gained many users or attracted major venture capital if its utility ended there.

It’s estimated that 6 million people use Twitter.com, up maybe sixfold from a year ago. Because the company doesn’t release numbers, measuring the Twitterverse is an educated guess.

Like any communications tool beyond cup and string, it gets more useful as more people use it. And as people and companies find new ways to put out information, the service keeps getting more interesting.

Useful applications

As with Facebook and the iPhone, the creative applications — the “apps” — various people have developed for Twitter improve it all the time.

The Museum of Modern Betas, an online “museum” of Web sites being tested, recently ranked the 100 most popular Twitter apps. Below are six of them, not the top six but a representative sampling of the amusing apps that Twitter users — not the inventors of the service — have been cooking up. Their ability to come up with words derived from “Twitter” or “tweet” is almost as impressive as their apps’ ingenuity:

• Twitterholic.com — With the tagline “Don’t your thumbs hurt yet?,” it ranks the leading Twitterers based on the total of their “followers” (although, remember, never judge your self-worth by that). The top 10 include very familiar names and some not-so-familiar: Barack Obama, CNN Breaking News, the English actor and comedian Stephen Fry, Twitter, tech innovator Kevin Rose, Britney Spears, The New York Times, Lance Armstrong, Twitter co-founder Evan Williams and Al Gore.

• Twellow.com — You can search all the Twittering on a given subject, everything from aerospace to cooking or motorsports.

• Twitturly.com — Tracks the Web sites that receive the most Twitter links that day — a snapshot of the subjects transfixing the world at the moment (or at least transfixing the people using Twitter).

• Twitscoop.com — Extracts the words mentioned often in hundreds of tweets a minute and turns them into “tag clouds,” visual depictions of what people are tweeting about. Theoretically, the cloud could alert you to something major going on slightly before the main news channels are attuned to it.

• Twitbin.com — Lets you scroll tweets down the side of your browser so you can follow them while you do actual work on your computer.

• Twitxr.com — You can send pictures from your mobile phone to Twitter.