Internet blog site Twitter, which allows users to post little 140-word blasts, is wildly growing and receiving comparisons to Silicon Valley's hottest real estate like Facebook and MySpace.  In March alone, it grew 131 percent adding 5 million new users. 

A new report from Nielsen Online, however, finds that approximately 60 percent of Twitter users quit after a month, never to return.  David Martin, the firm's vice president of research, says that while the endorsements of celebrities and public figures -- like Barack Obama, Jon Stewart, and Oprah Winfrey -- have encouraged many users to join, the site isn't keeping them coming back.

Mr. Martin states, "Twitter’s audience retention rate, or the percentage of a given month’s users who come back the following month, is currently about 40 percent. For most of the past 12 months, pre-Oprah, Twitter has languished below 30 percent retention."

The key problem, according to Mr. Martin, is that the low retention will eventually slow Twitter's growth to a halt.  There simply won't be enough users to replace the leaving ones at a certain point, he says.  Still, he says, Twitter won't die anytime soon, as successful sites' retention rates tend to go up.

He cites, "We found that even when Facebook and MySpace were emerging networks like Twitter is now, their retention rates were twice as high. (But) when they went through their explosive growth phases, that retention only went up, and both sit at nearly 70 percent today."

The biggest problem, Mr. Martin points out, is that people, by and large, tend to be quitters.  Microblogging daily requires a degree of dedication.  While it may be a valuable tool for social use and small business owners, most lack the kind of enthusiasm to sustain such efforts.  Twitter will have to struggle to make its site more fun and appealing to long term use, perhaps adding more options.