James,
I share your caution about social networks. They are a fun way to get/stay in touch with people. A good place to share my work and an occasional quip or two. But I'm very cautious about what information I publish on FB. Many of my "friends" there are merely acquaintances and some, I've never actually met. I have no desire to share my personal, political or other important views with them nor am I interested in theirs. If they're dog people, we share dog stuff. If they are photographers, we share photography stuff. Beyond that, the network doesn't show me a lot of value. Others have used it to market their businesses. I believe that they believe that it's been successful. I have not used it as a marketing tool directly but I have used it to illustrate my photographic skills and, indirectly, that has gotten me jobs that I would not have pursued otherwise.

It's like every other medium: you have to know what it can and cannot do and you have to be careful how you use it. I, too, worry about how much information the social networks collect on all of us. I worry about how they will use that information. Remember when we used to trust bankers and stock brokers to "do the right thing"? We were bitterly disappointed in learning that ultimately greed conquers reason. Let's hope the social network folks are better than that. But let's not lose our vigilance. Again.

Jim