Everyone has at least three personae. - the one you show to family members, the one you show to friends, and the one you show at work, and you may have more. Each one is authentic, but they're authentic to the specific context that you are in.
For example, I rarely swear at work - I have to be very frustrated or angry to do it there. A few minor words may slip out from time to time when I'm talking to family, but again, they don't hear it from me very often. On the other hand, with some of my friends I swear all the time.
In real life you can usually understand the context you are in pretty easily. Online it also used to be pretty simple - you would have one or more handles that you would use on different sites, and you generally acted appropriate to the image you presented using that handle. But now Facebook wants to combine all of that. They can present it as simplifying things for you - after all, you no longer have to manage all these different accounts right? But it also means that no matter where you are, you have to decide which "you" to present.
This is going to cause problems. --Those of us who understand the consequences are likely to either avoid sites that force you to authenticate through Facebook (this is my option), or start treating Facebook like Linkedin and do your best to prevent anything that may present you in an unflattering light to a potential employer. Young people aren't as likely to get this right away, and I fear that it's going to hurt them in the future.
Based on reading The Facebook Effect, I think that Facebook's change-the-world vision is to get rid of exactly this. It's part of what they mean when they say the world would be a better place if it were more open.
Zuck: They "trust me"
Zuck: Dumb fucks.
That infamous quote may in fact support the hypothesis, but it still doesn't quite feel right.
I am authentic in front of my friends, but I certainly act differently if I am also in front of everybody else.
The other really important thing people forget is that not only are you in front of either the whole internet or (merely) every acquaintance you ever had, but you are there permanently. Imagine chatting to your friends - now consider that you know the conversation is recorded and going to be stored where it could be held against you at any time. Would that alter your words? It certainly would affect mine. The non-recorded conversation is the authentic me, the recorded conversation is the careful, on-the-record me. That is why for me this sort of online conversation is never going to replace the real thing.
No. probably not.