Over half of Twitter users frequent the micro blogging site for just one month before getting bored of the service, says Nielsen Online.

"Let there be no doubt: Twitter has grown exponentially in the past few months with no small thanks to celebrity exposure," said David Martin, vice president of Primary Research at Nielsen Online, in a blog.

"People are signing up in droves, and Twitter's unique audience is up over 100 percent in March. But despite the hockey-stick growth chart, Twitter faces an uphill battle in making sure these flocks of new users are enticed to return to the nest."

Twitter has been having staggering growth in the last several months. Online traffic tracker comScore reported that Twitter had a 131 percent increase in US visitors just from February to March of this year. That came on the heels of another comScore report released earlier this month showing that Twitter traffic jumped 700 percent in February compared to the same month last year.

While part of Twitter's meteoric growth has been linked to an influx of middle-aged users, it's also been gaining a lot of mainstream media attention. Everyone from Oprah to Jonathan Ross have not only been Twittering but talking about it - a lot. Is this just because Twitter is a fledgling site that maybe hasn't found its footing yet?

Not really, according to Neilsen. Compared to the early years of social networking giants Facebook and MySpace, Twitter's retention is still bad. Both Facebook and MySpace had twice the retention rate that Twitter does now, Nielsen said. When their audiences ballooned, so did their retention rates. Both companies now have about a 70 percent retention rate.

"Twitter just doesn't seem to have a whole lot of stickiness to it," said Ezra Gottheil, an analyst at Technology Business Research. "People join Twitter ... and then it has to be an on-going commitment. Twitter's charm is that it's immediate and instant. The minute you get busy, its usefulness fades."

Gottheil also doesn't see any obvious solutions for turning Twitter's retention problem around.

"It's a major head scratcher because it's intrinsically a slice of time," he said, noting that when the influx of new users ebbs, the people quitting Twitter will really take a toll on the site.

"I hope they reach a phase of general stability. It has to level off at some point and it won't level off at everyone in the whole world using Twitter."