YouTube has more than 1 billion monthly visitors (full stats)

"Viewership
More than 1 billion unique users visit YouTube each month
Over 4 billion hours of video are watched each month on YouTube
72 hours of video are uploaded to YouTube every minute
70% of YouTube traffic comes from outside the US
YouTube is localized in 53 countries and across 61 languages
In 2011, YouTube had more than 1 trillion views or around 140 views for every person on Earth
Millions of subscriptions happen each day. Subscriptions allow you to connect with someone you're interested in — whether it's a friend, or the NBA — and keep up with their activity on the site
YouTube Partner Program
Created in 2007, we now have more than a million creators from over 30 countries around the world earning money from their YouTube videos
Monetization
Thousands of advertisers are using TrueView in-stream and 65% of our in-stream ads are now skippable
We have more than a million advertisers using Google ad platforms, the majority of which are small businesses
Mobile and Devices
25% of global YouTube views come from mobile devices
People watch one billion views a day on YouTube mobile
YouTube is available on hundreds of millions of devices
Traffic from mobile devices tripled in 2011
Content ID
Content ID scans over 100 years of video every day
More than 3,000 partners use Content ID, including every major US network broadcaster, movie studio and record label
We have more than eight million reference files (over 500,000 hours of material) in our Content ID database; it's among the most comprehensive in the world. The number has doubled in the last year
Over a third of YouTube's total monetized views come from Content ID
More than 200 million videos have been claimed by Content ID"
Source:  YouTube press statistics, retrieved 2nd April 2013
Earlier - Stats at 800m monthly users