Nearly one in five Internet users is tweeting on Twitter or using another service to share personal and business updates, or to see updates about others, according to a new study from the Pew Internet & American Life Project. That's an increase to 19 percent from 11 percent last spring, according to the group.

Pew attributes the Twitter rise to three types of Internet users: those who already are familiar with social networking sites, such as Facebook, LinkedIn or MySpace; those between the ages of 18 and 44; and those who connect to the Net wirelessly using mobile devices.

"I would have been surprised if we had not seen growth in Twitter and status updates since there is so much media coverage of it, from movie stars tweeting their thoughts to news anchors reading tweets on air," said Susannah Fox, associate director of the Pew Internet & American Life Project, and one of the authors of the study.

[...] "On-the-go Internet users say they like to share and communicate with other people — multiple devices make it easier, or inescapable. If you always have the means to update your status right there with you, tweeting can become a default mode."

The Pew study found that people who have four or more wireless devices — such as a laptop, cell phone, game console or e-reader like the Kindle — are the most likely to use Twitter, with 39 percent saying they do so, compared to 28 percent of users with three devices, 19 percent with two devices and 10 percent with one device.

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