The computer history blog ASCII lays out the meaning of Facebook in the grand scheme of things:
Facebook is the third of what is probably a quartet (or quintet) of the destruction of the innocence of computing. First was viruses, second was malware, third is facebook. I suspect fourth will be related to control of networking itself, and fifth will be licensing of high level computer ability. But let’s not get ahead of ourselves.
Facebook is a living computer nightmare. Just as viruses took the advantages of sharing information on floppies and modems and revealed a devastating undercarriage to the whole process, making every computer transaction suspect… and just as spyware/malware took advantage of beautiful advances in computer strength and horsepower to turn your beloved machine of expression into a gatling gun of misery and assholery… Facebook now stands as taking over a decade and a half of the dream of the World Wide Web and turning it into a miserable IT cube farm of pseudo human interaction, a bastardized form of e-mail, of mailing lists, of photo albums, of friendship.