Just who's using Twitter, and to what end? We're about to tell you, but the answer takes more than 140 characters — the limit for tweets.

Some 11 percent of U.S. adults who use the Internet also send status updates on Twitter, a three-year-old "communications protocol" that allows users to blast small bursts of info to their followers and friends, according to new data by the Pew Internet & American Life Project. Status updating is most common among young adults: 20 percent of 25-to-34-year-olds use Twitter, as do slightly fewer 18-to-24-year-olds. The results are based on a telephone survey of 2,253 adults.

Twitter, Yammer, Facebook and other micro-blogging platforms might be seen as just another way to self-promote. But more recently they've become journalism tools: reporters including those at ScientificAmerican.com use Twitter as a dedicated newsfeed to keep up with the competition (and, of course, to let colleagues and fans know about their latest stories — we're at http://twitter.com/sciam). We also use Twitter to keep up with our readers, and to solicit ideas from them — to great success during last month's perigee moon. In other instances, non-media people are using it to "report," as well, even if they don’t think of themselves as journalists: a photo of Flight 1549 that crashed in the Hudson River last month instantly became iconic after Janis Krum sent it out over his Twitter feed. On Wednesday, the ShortyAwards honored the most talented Tweeple (or, some might say, Twits), including the Mars Phoenix, which tweeted its demise from the Red Planet.

"It's a tool like we've seen cell phones become a tool in reporting," says Susannah Fox, an associate director at the Pew project and a co-author of the report. "Back in the day, people would snap a picture because they were on the scene. [Now] there's a proliferation of ways to capture what's happening and to broadcast what's happening. The velocity of this kind of sharing is speeding up. It's not a new phenomenon, just more widespread."

That said, many Twitter users embrace the technology as a way of feeling "ambient intimacy," Fox says, just as people share the details of their lives with those far away via the telephone, email and blogging. "What's new about it is the ability to communicate with so many people at once. What's not new about it is you can create niche audiences just like we've been able to with blogs, with listserves back in the day. Twitter and status updating in general is another link in the chain of what we've been seeing the last 10 years."

But if you're annoyed by the content of the tweets in your feed, don’t blame Twitter, Fox says. "New technology is often praised or blamed for human foibles that are universal, whether it is the telephone or social networking sites or now Twitter," she says. "In the hands of some, it will be a tool of self-promotion and for some, other pursuits."

Updated at 6:05 p.m. Feb. 13 with additional context about uses of Twitter.

Image © iStockphoto/Oktay Ortakcioglu