Facebook's squarish, sans serif, gothic-inspired font is a customized version of a type called Klavika, developed in 2004 by a designer in England.
"In the same way that Facebook represents the culture and technology of a decade, Klavika does the same for typeface design - well crafted but blatantly simple, monolinear, square, nearly devoid of any calligraphic ancestry."
Movie posters for "The Social Network" also make use of this typeface:
And NBC is using a relative of Klavika now too:
