Facebook has >400m active users

"Company Figures
More than 400 million active users
50% of our active users log on to Facebook in any given day
More than 35 million users update their status each day
More than 60 million status updates posted each day
More than 3 billion photos uploaded to the site each month
More than 5 billion pieces of content (web links, news stories, blog posts, notes, photo albums, etc.) shared each week
More than 3.5 million events created each month
More than 3 million active Pages on Facebook
More than 1.5 million local businesses have active Pages on Facebook
More than 20 million people become fans of Pages each day
Pages have created more than 5.3 billion fans

Average User Figures
Average user has 130 friends on the site
Average user sends 8 friend requests per month
Average user spends more than 55 minutes per day on Facebook
Average user clicks the Like button on 9 pieces of content each month
Average user writes 25 comments on Facebook content each month
Average user becomes a fan of 4 Pages each month
Average user is invited to 3 events per month
Average user is a member of 13 groups

International Growth
More than 70 translations available on the site
About 70% of Facebook users are outside the United States
Over 300,000 users helped translate the site through the translations application

Platform
More than one million developers and entrepreneurs from more than 180 countries
Every month, more than 70% of Facebook users engage with Platform applications
More than 500,000 active applications currently on Facebook Platform
More than 250 applications have more than one million monthly active users
More than 80,000 websites have implemented Facebook Connect since its general availability in December 2008
More than 60 million Facebook users engage with Facebook Connect on external websites every month
Two-thirds of comScore’s U.S. Top 100 websites and half of comScore’s Global Top 100 websites have implemented Facebook Connect

Mobile
There are more than 65 million active users currently accessing Facebook through their mobile devices.
People that use Facebook on their mobile devices are almost 50% more active on Facebook than non-mobile users.
There are more than 180 mobile operators in 60 countries working to deploy and promote Facebook mobile products"
Source: Official Facebook Statistics, retrieved 9th February 2010.
Earlier figures here (>350m active users, December 2009)