2.6 billion minutes are spent on Facebook each day worldwide

"Average user has 100 friends on the site
2.6 billion minutes are spent on Facebook each day (worldwide)
More than 13 million users update their statuses at least once each day
More than 2.5 million users become fans of Pages each day
More than 700 million photos uploaded to the site each month
More than 4 million videos uploaded each month
More than 15 million pieces of content (web links, news stories, blog posts, notes, photos, etc.) shared each month
More than 2 million events created each month
More than 19 million active user groups exist on the site"
Source: Facebook Press Statistics, retreived 20th December 2008
Updated here