Uh, that sounds like a privacy nightmare. Well, one could argue that existing social networks are already a nightmare, I guess. So much of the damage is already done.
Inevitably the solution will be a decentralised social network which other providers can tap into - core functionality such as profiles (and location?) should be as portable as a wordpress blog: either I get someone else to host it or I host it myself.
If my "friends" know that I'm hiding something from them, they feel bad, and they may not be my "friends" for much longer.
I would hope that my friends don't feel left out if they aren't getting my complete output stream. If someone did, I would find it odd and possibly creepy depending on the context.
But it probably depends on whether people use social networks for managing a broad range of contacts or to keep in touch with close friends and family.
The general problem is that some things can change dramatically as soon as they become explicit, even when nothing of substance has changed.
One profile to rule them all sounds great, but read ths http://www.plausiblydeniable.com/opinion/gsf.html