Facebook users now number 300 million—nearly the size of the US population—CEO Mark Zuckerberg announced on his blog Tuesday. What's more, he said, Facebook is now in the black, well ahead of his earlier prediction that the company would reach profitability in 2010 at the earliest.

Hitting the 300 million mark was "just a matter of time," writes TechCrunch's MG Siegler, who notes that the site had 250 million users in July. Gaining 50 million users in two months amounts to a growth rate of more than 800,000 new users a day, CNN points out.

Starting the year with about 150 active users, Facebook has doubled its user base in little more than nine months, writes Los Angeles Times blogger David Sarno.

About Facebook's phenomenal growth, Zuckerberg said in Tuesday's post: "We're just getting started on our goal of connecting everyone."

Some 70% of Facebook users live outside the US, according to the company. Although Facebook started as a way for college students to connect with one another, people 35+ are now its fastest-growing demographic.