Personally I don't believe much of the privacy claims that the social networks assure us of. In fact I don't believe that ethics matter to them at all. Making money is their ultimate goal.
Once you have joined them, you decide the amount of information you want to put on your profile.

Remember that "Advertisers" are their clients, not you, the free member!
Have you noticed that as soon as you have joined one of these sites your spam e-mail jumped up dramatically? They promised to keep your information private (including your e-mail address), didn't they!!!
Who gave these advertisers your e-mail information?

Among all social networks, my enemy number 1 is Facebook. I simply hate that site, and I know some are worse (like MyLife, MyYear Book, if I'm not wrong about the exact names), but these are less popular.

I hope Google is not going to become another Facebook.

I have been a premier G-Mail member (since they started offering e-mail accounts, years ago), and I have received the invites to join Google+ (among other "Googlings"), and I am glad I never joined any of them.