How safe is to give your personal information on websites such as facebook, my space and any others? What’s the limit for you?

I am really into social media and I have seen on people’s profiles information such as contact details, family members, addresses, which I think is very dangerous. I have always been careful about the information that I share in social networks because I´ve never trust them, at the end of the day you will never know who is behind the screen. I think that if you want to protect your personal data, the limit is on specific personal information such as date of birth, occupation, places that you frequent, family members and others.