Can we keep our life private?

You know, I faced a new situation for me. I just reallised how much you can know about a person who is active on-line. Or even you don't have to be active, but you just participate in different events and then report from those events is on-line, so you are present there as well. Sometimes it's really fun, as you can find out about your new friends a lot even before they will tell you. BUT. If it concerns you, then you start to think what you want people to know about you and what you don't. Today I got a message from my friends that they discovered my blog although I have never told that I had one. So in a way it's great and fun, but on the other hand it a bit scary... :)