Right now, we can see such sign "become our fun on Facebook" on more and more sites. (We may be one soon.) Even when we visit local restaurants, we see "facebook" on menu. At a conference in France last month, Facebook CEO Mark Zuckerberg said the site will reach 1 billion users sometime next year.
However, some people challenge it now, "Two thirds of those 'users' are individuals with multiple accounts for Mafia Wars, FarmVille, etc. In five years nobody will use Failbook. It is the next Friendster! " (source: http://www.businessinsider.com/are-a-third-of-facebooks-users-fake-2010-7)
Are A Third Of Facebook's Users Fake?