• AFP, Wednesday, April 29, 2009 11 AM

Twitter's phenomenal growth has been well documented, but its month-over-month audience retention rate is a mere 40%, says Nielsen Online, meaning that more than 60% of its users fail to return the following month.

By comparison, Facebook and MySpace have retention rates of nearly 70%. "Twitter has enjoyed a nice ride over the last few months, but it will not be able to sustain its meteoric rise without establishing a higher level of user loyalty," David Martin, Nielsen Online's vice president for primary research, said in a blog post.

"Let there be no doubt: Twitter has grown exponentially in the past few months with no small thanks to celebrity exposure," Martin said, referencing new users such as talk show host Oprah Winfrey and actor Ashton Kutcher. Martin noted that new users continue to sign up "in droves," and that Twitter' unique audience was up more than 100% in March. Even so, the microblogging sensation faces "an uphill battle" in retaining these users, Martin said.

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