I am extremely careful about posting anything sensitive to the one "social" site I use - LinkedIn. Personally, I do not see LinkedIn as a "social" site. I see it as a "professional" networking site that just might get me a job some day, and in fact, I likely would have found a job through there if I had not found my current job elsewhere first.
I do not use the other "social" sites. The whole world does not need to know every detail of my personal life. Besides, I have things that I consider more important.