• 72.5% of all users have joined since January 2009
• 85.3% of all Twitter users post less than one update per day
• 21% of users have never posted a Tweet
• 93.6% of users have less than 100 followers, while 92.4% follow less than 100 people.
• 5% of Twitter users account for 75% of all activity
• New York has the most Twitters users, followed by Los Angeles, Toronto, San Francisco and Boston; while
• Detroit was the fast-growing city over the first five months of 2009
• More than 50% of all updates are published using tools, mobile and Web-based, other than Twitter.com.
• TweetDeck is the most popular non-Twitter.com tool with 19.7% market share.
• There are more women on Twitter (53%) than men (47%)
• Of the people who identify themselves as marketers, 15% follow more than 2,000 people. This compares with 0.29% of overall Twitter users who follow more than 2,000 people

Interesting facts about Twitter‘s current user base, perhaps it will look much different in 6 months.

The “microblogging” site drew 18.2 million users in May, up 6.7 percent from a month earlier, according to New York-based research firm Nielsen Online. Twitter logged 7.04 million users in February, almost doubled that to 13.9 million in March and then gained 23 percent to 17.1 million in April, when Winfrey signed up for the site on the air.

Twitter’s slowdown was expected because the pace it set in March and April was unsustainable, said Andrew Lipsman, a spokesman for Reston, Virginia-based ComScore Inc., another Web audience-ratings service. While ComScore’s final May data isn’t done yet, weekly surveys by the researcher show Twitter’s usage peaking at 6.78 million people in early May and dipping to 5.46 million by the week ending May 31.

“We saw huge growth, and a lot of that had to be trials,” Lipsman said. Some of the audience may have also shifted from visiting the site itself to using Twitter-related software tools. They let people post Twitter messages without showing up in usage statistics for the company’s home page.

In response to the report, Twitter said it’s investing in areas that will fuel growth in the long run.

“We have a lot of work to do,” said Jenna Sampson, a spokeswoman for San Francisco-based Twitter. “We are still a young company and very much focused on growth. We want to mature properly.”

It’s probably a good thing that traffic has slowed for a while, which will give the Twitter team a chance to catch their breath before the next wave of traffic hits.