Twitter hasn't gone completely mainstream, but its traffic figures have gone up as several bloggers, media outlets, and at least one campaigner have taken notice of the site.

The market share of visits to Twitter, a Web site that allows people to send brief text messages to groups, grew by 55% last week, compared with the week before, according Hitwise research director LeeAnn Prescott, who noted the trend in her blog Monday. Prescott labeled the site "one to watch."

She isn't the only one keeping an eye on Twitter. Obvious Corp., the company that runs the site, has issued statements indicating it is trying to increase server capacity to keep up with growing demand. Among the notable Twitter users -- sometimes called Tweets -- is presidential hopeful John Edwards' campaign, which uses it to "Twitter-patter," that is, post information on his schedule.

The site launched less than a year ago and has drawn 60,000 users, who essentially tell each other what they are doing -- like Google's Dodgeball. Users can send messages from PCs, mobile phones, and other devices messages for free. The information goes to people they allow to be "followers."