But since the middle of last year, the number of Twitter users has flatlined.

Compete, a Web analytics firm, says the microblogging site's number of visitors hasn't changed much since June and that its roughly 22 million visitors in December was about 770,000 fewer than its highest number, which was in August.

Multiple other analysts paint the same picture, raising the question: Has Twitter peaked?

"Maybe Twitter was a victim of its own success," said Andrew Lipsman, an analyst at comScore, another company that tracks traffic on Internet sites. "It grew so quickly that it isn't meeting its own expectations."

But the company and some analysts say that this leveling of popularity shouldn't be viewed as a failure, because the people who use Twitter are using it more than ever.

ComScore's usage numbers for Twitter are similar to Compete's. They show the site peak with about 21.2 million visitors in July 2009 and dip to 19.9 million in December. By contrast, during the same period Facebook grew from about 250 million users to more than 350 million.

Lipsman suggests Twitter's recent stagnant numbers look anemic largely because its growth in early 2009 was so astronomical.

After several months of double-digit growth, traffic to Twitter.com skyrocketed in March, increasing by 131 percent in just one month.

That was the sharpest spike in a growth boom during which, according to comScore, the site went from about 2.6 million visitors at the beginning of January 2009 to 17 million by the end of April.

"I was really floored when I was watching those numbers come out," Lipsman said. "I've never seen anything close to that in the natural growth curve of a site."

Interest was piqued after celebrities, athletes and other high-profile users signed on early last year, sharing their thoughts with the world in 140-character snippets.

Source ---> http://www.cnn.com/2010/TECH/01/26/has.twitter.peaked/index.html