No seriously . . . A few years ago, i guess 06, all my jacked-in friends were making the move from myspace to facebook, and people i knew that were less jacked-in were registering. Everyone was on me like 5th grade cigarette smokers "dude it's cool, everyones doin it" but i never got around to regging. Never cared that much.
Today, those same people hate facebook. They're bored of it and they've finally had it. They've discovered that it's a time sink, the connectivity is largely worthless as well as hard to keep up with, and the negative publicity certainly doesn't help.
All of a sudden, the people that were calling me antisocial a couple years ago are now calling me prescient . . . that I somehow saw the whole thing coming. The truth? I just didn't care. Still don't. I've got about 8-10 people that I really care about in the world and i'd just as soon go over to their house and look at their dog for real. My son, otoh, has adopted a friend-removal doctrine... "When i get a notification for your birthday, if i wouldn't care enuf to actually call you and say 'happy birthday', then i'm removing you." Solid.
Anyway, I can't answer the question, but I can give an answer: It was cool at first, but now it's just too much of the same thing. all the features and crap that have been added, from what i've seen and heard, have cluttered up the interface. by contrast, when gmail adds features, they barely touch the core of the app and add things that make it easier to use the core of the app. Facebook could learn a thing or 2 about that.
Google = Diversify and Focus. A billion different apps that do one thing. cool. Facebook = Focus on diversity. One app that does a billion different things? not cool.