I'm confused, how is the founder of Facebook a person of the year? The first time I heard of him was cause of the movie, and that hardly makes someone person of the year.
Because of the sheer level at which Facebook has permeated and altered society and social connections. It's kind of hard to explain how immersive it is to people who don't use it, but the way I always think about its impact is this: The feeling of realizing you've lost touch with a friend? How they could be anywhere and anyone after all these years and you'll probably never know? You know how affecting, and universal, that feeling is?
Every generation after this one might not.
Stack that with all the other things it's become indispensible for(sharing photos, planning parties and events, discovering the obscure interests you have in common with friends and probably wouldn't have realized otherwise, even stuff like bridging the gap between celebrities and fans to an extent no one would've thought possible until now, although Twitter's probably taken over as #1 in that last one) and the sheer numbers involved at this point(a twelfth of all humanity uses it, including the US President and the Queen of England, and the percentage is growing. If it were a country it would be the world's third largest. In a predicted year or two, more people will have a page than will be hungry-via-poverty), I think it's pretty cut and dried how notable it's become.
I probably couldn't have told you Zuckerberg's name until about a year ago, but most people probably couldn't name Guten
berg either, even people who'd agree he was the most important person of the last thousand years once you told them. Same with Bell or Borlaug or Tesla. Influence doesn't always equal fame.