Yep, I agree with Honestman too.
I found it useful for catching up with old friends and reminding me when friends (actual friends) birthdays were coming up. But then I realised there's a reason I haven't seen so many of these 'old friends' in years; They're not friends. Life goes on, people drift apart. High School was great... but it's over. And it's been over for a long time (for me). Some people haven't got the memo yet.
I left facebook about 3 years ago. I had 50 'friends'. I believe in facebook terms, that's pathetic! Everybody now and even back then had 200+. I never added randoms. But even from those 50, I'd say I'd cross the road to avoid about 40 of 'em. That leaves 10, 10 people I genuinely consider friends. Which in real world terms isn't bad.
I quit when I found myself reading some incredibly inane status update by a friends friend which I didn't really know and judging by her activities on facebook, I really disliked. Enough was enough. What a fucking waste of time. All the time I spent reading her and other peoples bullshit I could have been reading a fucking book! Exercising my brain. Learning things.
Haven't looked back since.
My teen nephew is a facebook kid. Literally spends his whole day on it. He usually falls asleep with his laptop or iPad, sometimes both! Sometimes I think he's borderline autistic. Can't look away from the screen and actually talk to people. He is or at least used to be such a great kid. Really pisses me off. And I tell him so. But yeah, he's not really listening... cos he's too busy on fucking facebook!