Thursday Clubs post on Facebook Statistics is excellent, showing the total number of Facebook users at 42,966,780 people or 0.6% of the worlds population. I took his top 10 countries and made a table with the respective country populations (taken from Wikipedia).
As you can see we in in the UK are in bronze position with Canada taking the gold and Norway silver. The USA where Facebook originated is way down at sixth position.
An impressive achievement since Mark Zuckerberg launched The Facebook in February 2004 and only purchased the facebook.com address in August 2005 .