Facebook underwent two massive shifts in 2011, the details of which are hidden in the company's S-1 filing.
At the beginning of the year, the fast-growing social network had most of its users in the U.S., Canada and Europe, the regions where it got its start.
By the end of the year, most Facebook users were elsewhere -- in Asia, Latin America, Africa and the Middle East. What's more, that shift continues: Emerging markets grew three times faster than the U.S., Canada and Europe in 2011.
That wasn't all. At the beginning of the year, a third of Facebook's users accessed the service through a cell phone or another mobile device at least some of the time. By the end of the year, more than half did.
Many of the numbers come to light on page 44 of Facebook's S-1, where it charts the locations of its monthly active users. A Facebook executive told CNBC in late 2010 that a third of Facebook's user base accessed the site through mobile devices; the S1 notes that more than half of Facebook's 845 million users accessed it through a mobile device in December.
The significance of the changes? Facebook says its goal is to connect all of the world's Internet users, and increasingly those users are joining from outside of Facebook's original markets and on devices that are difficult to monetize. (Facebook's ads and apps don't run on phones the way they do on computers.) To reach a billion users, a mark Facebook might hit late this year or early next, Facebook will have to continue growing in emerging markets in particular. And to grow revenue, the company must figure out how to offer advertisements on mobile devices that don't annoy users.