In terms of individualized usage of an online service, this is a staggering milestone.  Facebook is expected to announce soon that more than 500 million people have signed up for an account its site, despite recent privacy concerns.  That is approximately one in every twelve people on the planet (approximately one in four Internet users worldwide).

Besides the total number of users, Facebook’s rate of growth is also pretty amazing, having just announced in February that it had exceeded 400 million users.  At this rate, it’s doubtful that “Quit Facebook Day” will even cause a blip in the company’s growth charts.