There are issues with social networks that can create opportunities for people to observe too much information. Looking at a couple of specific instances recently, this has really been made clear to me.
Especially if you are signed up for social networks, its worth searching for your own name, and ensuring you are comfortable with the results.
Technorati tags: social+networks, privacy
Bankwatch 
Yes, you’re right, particularly from a security standpoint. Eg, I’m aware of cases where people that work in highly secure areas (like a vault) list information about where they work, where they have lunch, etc. People need to use good sense.