Twitter CEO Dick Costolo 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."

Read the full story at The Atlantic Wire.