Social networking sites are disasters. Social networking sites are nothing more than tools for narcissists. Social networking sites are increasing in popularity but are really destroying natural and healthy interpersonal relationships and foster ignorance of the human condition. Take this example, recently two girls fell into a sewer and though they had their cells phones with them, didn't have the common sense to call for help, instead they just updated their Facebook pages until someone figured out they were in trouble and called help for them.
No, they can have a negative affect on people's 'real' life. A lot of people these days are so caught up in things on social networking sites there not paying attention to all the things that are happening around them. I mean when was the last time these people went out and physically talked to someone rather than messaging them on Facebook. Another thing is how many of your friends do you really personally know? Isn't a friend someone you can trust and you respect and would stick up for not just someone you just meet on line?