YouTube has over a billion viewers each month

"In the last eight years you’ve come to YouTube to watch, share and fall in love with videos from all over the world. Tens of thousands of partners have created channels that have found and built businesses for passionate, engaged audiences. Advertisers have taken notice: all of the Ad Age Top 100 brands are now running campaigns on YouTube. And today, we’re announcing a new milestone: YouTube now has more than a billion unique users every single month.
What does a billion people tuning into YouTube look like?
- Nearly one out of every two people on the Internet visits YouTube.
- Our monthly viewership is the equivalent of roughly ten Super Bowl audiences.
- If YouTube were a country, we’d be the third largest in the world after China and India.
- PSY and Madonna would have to repeat their Madison Square Garden performance in front of a packed house 200,000 more times. That’s a lot of Gangnam Style!"

Source:  YouTube blog, 20th March 2013

Earlier - 800m uniques still being reported in early March 2013