Is Twitter the next Second Life?

Lance Armstrong loves it. Oprah's all over it. Ashton Kutcher found a million people to follow him on it. Heck, Barack Obama used it to get elected president. So why is Twitter in trouble?

According to David Martin, Vice President of Primary Research at Internet traffic monitor Nielsen Online, the site suffers from a retention problem. From month to month, Nielsen data says, just 40 percent of Twitter's users return to it.

The microblogging service has been the tech darling of late, racking up new users at a dizzying pace. When daytime diva Oprah became a user live on her TV show earlier this month, the site saw a 43 percent increase in traffic, Hitwise reported.

But the Oprah crowd – and thousands of new users like them – aren't coming back nearly as often as they need to be if Twitter's growth is to be sustained, writes Martin.

"There simply aren't enough new users to make up for defecting ones after a certain point," Martin says in his blog post.

In supporting his argument, Martin looks at MySpace and Facebook from when they were new on the scene like Twitter is now. This chart shows that at similar times in their lives, the two social networking giants had double the retention rates Twitter has now. And, as fans are quick to point out in fields of comments around the Web, Facebook offers so many more ways to interact.

Still, maybe numbers don't tell the whole story.

As John C. Abell points out in Wired, people interact with Twitter in many more ways than just visiting twitter.com.

Cooks are publishing recipes 140 characters at a time, and ferries telegraph their comings and goings, and scientists use it to send telepathic messages, and guilt-ridden souls confess anonymously, and audiophiles turn it into a music discovery engine, and politicians are announcing their candidacies and even tweeting from the House floor, he writes.

As many of the its users are quick to point out, Twitter would exist even without the website – on mobile phones (the source of that pesky – or perfect – 140-character limit) and through standalone applications like Tweetdeck. And for those that "get it," the service's utility remains, regardless of numbers.