I'm very open on the internet. It doesn't affect me if strangers know my business because they don't care and I'm not so grandeur to think that someone would ever stalk me.
I don't tell anything to anyone I know, though. I keep my opinions about everything to myself. The most my family and friends could tell you about me is that I like animals. I prefer for those closest to me to know absolutely nothing about me because I don't trust anyone and everyone I know is supremely judgmental, gossipy, and close-minded for the most part. Even my facebook page has no information about me and I delete anything I post on facebook within a few days after posting it, although around christmas I filled in my religious status as 'Atheist'. I revealed this out of anger at the bigotry I was seeing all over facebook, but no one noticed so there was no point anyway.
I suppose my version of the adage "Keep your friends close and your enemies closer" would be "Keep strangers close and keep your friends miles and miles away."