I don't really use social media, but I had a FaceBook until 1 year ago. When I was active I had ~1,100 friends. I realized that aside at most 10%, I wasn't at all concerned about the day-to-day activities of these "friends" and the people who posted the most are the people cared the least about. The people close to me I already keep in contact through conventional modes of communication (real life interaction, phone, email, text, Skype, FaceTime). I concluded if I want you in my life, I will be in contact with you. Conversely, if you want me in your life, you can reach out to me. In hindsight, I'm not too sure belonging to FaceBook really enhanced my real world social life to any degree and mostly served as a contact list of every young person I've met in 8 years. The benefits I experienced was exposure to new ideas and concepts and a way to stay in touch with distant friends and family, like my relatives in Israel. That said, for me FB is not enough to maintain a quality relationship and the disadvantages outweigh the advantages.
Being completely honest, the biggest problem I had was just the amount of anxiety and insecurity in bred within me. The effect is well documented in studies. I was constantly judging myself and comparing my life against the virtual representation of others' lives (which are usually glamorized, idealized, etc). In addition to content, there were quantitative metrics like number of tags, pictures, friends, likes, etc to analyze. I could easily slip into a sense of inferiority comparing myself to others which highlights my own insecurities. At the same time, likely to compensate, I could criticize others based on their content or statistics. For people I disliked, I could find additional reasons to justify my dislike. Interestingly, looking at my close friends and family did not evoke the same emotions. That said, knowing I was open for behind-the-back criticism, my anxiety increased about what and how I presented, not to mention how people responded. All of this negative energy is not something I want to feel or express towards others.
Sure, you and I can judge people in real life, but face to face there is distraction to take away from the judgements and factors to alter your judgement- like a context, emotion, and an environment. In real life out of politeness we hold back judgement (criticism, eye rolling, laughing), but in social networking we can make our judgement and instantly send the exact information to others, and later go back to it, to further reinforce the negative ideas. Ironically, in some ways virtual world is so much more physical than the real world. In real life, events begin and end, while online pictures, videos, and posts can be downloaded and/or shared. I have personally seen classmates and fellow employees disciplined for what they have posted online, not limited to firing people with professional degrees.
If I ever return to social networking (to keep in contact with people far away from me), I will put more planing into building my network. I will only accept friendships with people I am actually good friends with in the real world. My recommendation, is to do the same. Figure out what your intentions are with social networking and execute accordingly. If it's for your friends, make sure it's your actual friends. If it's for your career, keep it professional and don't intermingle your personal life. The free-for-all, have-as-many-friends-as-possible approach (in my experience) serves no benefit in my experience.
I recently attended a psychiatry conference with excellent MD speaking on the internet/social networking on mental health. I've written too much already, but his general opinion was negative regarding FaceBook, for some of the reasons I mentioned here. His concern was focused most upon the youth and young adults. He had quite a few studies to back up his thoughts. More on that later...