My sister lives in Italy with her family. My uncle lives in Germany, my cousin lives in Japan, I have friends (not "facebook"-style friends, but good ones I met in real life) in Australia, New Zealand, South Africa to name a few countries.
Social networks allows us to keep in touch and communicate. Sure, you could do that by placing a phone call and sending letters and e-mails, but it would be more complicated (timezone differences and whatnot).
With that being said, I'm not the usual facebook dweller. I only access it when needed, my circle of friends is indeed composed of friends and relatives, not the random dude who added you and never interacted with you again. And yes, i shudder when i see people checking Facebook on their mobile phones every other minute. I for one don't have it installed, nor would I ever do such a thing.
I guess I'm trying to say it's okay to use social networks as long as you don't let the social networks use you.