Twitter CEO Dick Costollo spoke to a room full of journalists and a world full of Twitter users Thursday in one his semi-regular "informal" business addresses. Big news: Twitter has reached the 100 million active user mark. Though they've bragged about all sorts of stats in the past, this is the first time that Twitter has publicly disclosed their total number of active users. Important detail: nearly half of those "active" users do not tweet. "For many, getting the most out of Twitter isn’t only about tweeting," explains the official Twitter blog. "40 percent of our active users simply sign in to listen to what’s happening in their world."

The breakdown of those that do tweet is pretty interesting, and based on the fact that Twitter spent the majority of their announcement blog post focusing on their demographics, they're proud of whom they attract. Danny Sullivan rounded up these numbers and tons of others at Search Engine Land:

Of those 100 million…

  • Every team in the NFL is on Twitter and more than 50% of NFL players
  • 75% of NBA players
  • 82% of the US Congress and 85% of US Senators
  • 87% of the Billboard Top 100 Musicians of 2010
  • 93% of Food Network chefs
  • 100% of the top 50 Nielsen-rated TV shows

Conspicuously missing from Costollo's business address was serious talk of the company's revenue numbers. "We should think of revenue as the way people think of breathing, it's necessary for life but it's not the purpose of life," Costollo said. (Translation: Twitter still has a lot of venture capital money.) He added that Twitter is working hard to boost advertising on the site. "That's the only thing we think we need to do to be a successful business," he said. The company announced in July that the company would be putting ads in users' Twitter streams, but they haven't said much about how that's going. With Facebook doubling its revenue year over year, Twitter's investors will surely soon want to see some hard numbers on their bottom line, regardless of how many celebrities they have signed up.

By the way, Sina Weibo, that Chinese Twitter knockoff, is catching up in terms of users. And they're coming to the United States.