Both are kind of correct. Twitter, which has been historically stingy about sharing statistics, said in a blog post yesterday that the service has 200 million registered accounts and 100 million active users, active being defined by people who log in once a month at least. Of those 50 million log in every day. Some more math: 40% of the active users are passive once they get on the site. They read, they don't tweet. Also: Each of the 50 top-rated Nielsen TV shows has a Twitter account, as do 87 percent of top Billboard-rated artists. Two-thirds of the NBA are active on Twitter, and every team in the NFL, MLB, NBA, NHL and MLS has an account.