Sounds like google's circles. The problem is that most folks treat their Gmail account as their "real" account and don't give it out willy-nilly. Also, that the circles thing is one-way - I can use circles to control how I see others, but can't use them to control how they see me.
> Also, that the circles thing is one-way - I can use circles to control how I see others, but can't use them to control how they see me.
No, if you share something to a circle someone isn't in they wont see it, so they do let you control how others see you. Not a huge G+ fan, but I was a fan of circles.
I was not that big fan of circles, made sharing with the wrong people easy.
I like that my personal life (facebook) and professional (linkedin) is two different networks. Its hard to accidentally share the the bad joke with my professional network.
I think something like circles could be done right -- if each circle had a custom background, etc. so that it looked and felt like a different website. I'm not worried about posting political rants to LinkedIn because it's obvious I'm on LinkedIn rather than FaceBook or Google+; I wouldn't be worried about posting to my coworkers group if there were very obvious signifiers that I was in that group.
IIRC, Facebook used to have this feature (ages ago), but it was removed. It used to ask where you knew someone from when sending a friend request, and it didn't let you send the request if you didn't know the person.
On the profile page of your contact there is a "★ Relationship" button. Click that and it will let you add general notes or more detailed information about how you met.
Would you trust them enough to be certain enough that it would always stay this way so you could safely put slanderous information about a person here? I certainly wouldn't.