And I'm only talking about information I explicitly put there. I didn't talk about what could be inferred from that, which can be quite a lot. Even more so when this information is centralized so it can be compared to the other users'.
> Can anyone think of a case where someone's life was significantly impacted by the exposure of private information online?
To convince you, I feel I would have to point to a case where someone's live was suddenly impacted. It does happen, but the main impact is probably more subtle, like discriminations (which you can't see) or advertising (which can do a better job influencing you).
The real differences lies in the understanding of the risks. The "brother bartender" is something most can understand. We all understand that talking in public areas carries a risk of being overheard, and we tune our speech accordingly. However, we don't all understand the risks associated with Facebook and many other services "in the cloud". This means a higher risk of being careless (and hurt yourself in the process).
Until we understand privacy risks associated with internet services as well as those associated with physical interaction, we will have unexpected problems. I'm confident that people will learn anyway. I just hope they don't learn the hard way.
People "volunteer" information about themselves online without intending to or without being aware of what they are revealing (or what Facebook et al will do with it) and what is or is not considered an invasion of privacy is a largely arbitrary social construct. That is why these are real issues, and the answers are not as trivially obvious as you seem to think.
Someone taking a picture of your street and putting it on the internet doesn't violate your privacy. Someone making use of information that you volunteered to a social networking site doesn't violate your privacy, either. Online advertising relates to privacy in only the most extreme of cases - where somehow spyware is installed on your computer that records what software you use and how you use it. Tracking cookies do not violate your privacy.
If you legitimately have something to hide, you won't be found out by online advertising, facebook or even google. There is very little online that can gather information about you that you don't volunteer in some way. Can anyone think of a case where someone's life was significantly impacted by the exposure of private information online?