Very cool question and observation!
I think just a specialist or psicologist can responde with facts, but in my opinion is true, this "social networking" has that effect, to become people anti-social, but not only antisocial, I notice (almost in Mexico) people use those services to collect people, Yes! use them as collection, I mean, they search in the "service" for cute faces, then send an invitation to be a "friend" but they never spoke with you, or just say: hey hello, bye im busy! you dont care them at all...just want to be "popular"...
The worst effect but also the most interesting is the capability of this services to "show" the real face of the people whom try to hidde them in a fake profile, for example: How many "profiles" can you identify where the picture is a Top Model or a girl with an awesome body, but obviously fake, then read the profile saying: I'm the best damn think you can find in the world, but you try to "get connection" but never responds... Is a massive "issue"; the actual people have the worst self-esteem, they are so materialist and hypocrite than forget the real meaning of "socialize" showing who you really are...
Finally, I guess Microsoft's stake is not yet enough.