James,
I may be a photographer, but I've spent a lot of time as a marketer and I realize that the most important part of marketing is data mining. And that's what the social networks are there to do. They do it insidiously by providing a forum for sharing, but what folks are sharing -- lifestyle data -- the social networks are collecting and using to attract advertisers who want and need (and can pay for) highly targeted audiences.
We are still active doing advertising/marketing for several corporate clients. Our largest one develops school/college/organizational "directories". Most of their work is online and/or mobile-based these days but the products are seldom what the end-users perceive them to be. They are data mining for fund-raising. And every application they develop collects information about the end-users that then helps the schools/organizations do a better job of targeting their donors. So I have a pretty intimate view of how much information can be collected via apparently "innocent" social media.
Does this cause me pause? Yes, it does. Does it cause me to be paranoid? No, it doesn't. I realize I have to be careful and I try to be careful. But, ultimately, you take a risk every time you join a forum or send an email or test message. There is no personal privacy. So just be careful to make sure that what people see is what you want them to see
.
Jim