The Problem With Social Networks: Multiple personalities.
All of us - as human beings - have many aspects. We come in many flavors. That’s what makes human interactions so complex and interesting.
There is a Working-You, a Family-You, a Friendly-You…
More than that, for each one of these Yous_ there are different versions.
At work, you don’t behave the same with your boss’s boss and with your co-worker in the next cubicle.
With family, there is the yearly great-great-aunt’s family reunion You, and the Sunday’s garden Hot Dog party with your 3 brothers and their wives and kids You.
The same goes with friends.
Then there are the places. If you’re in the street, in a theatre, in a cosy restaurant, or at home, you won’t behave exactly the same.
All this is for a regular quiet life.
It gets trickier when there’s your wife’s You and that cute little blond girl you met at work’s You…
Topics of conversation, vocabulary, plain behaviour, won’t be the same.

This guy I work with (or more precisely, I work in the same company as he), sends me an invite to be friend on Facebook.
Two options: trying not to be rude, accepting the invite OR being consistent, refusing the invite: WE ARE NOT FRIENDS.
(I’m not talking about the networking use of Facebook - interesting thought by Seth Godin here though).
Or
This great conversations I have with my WOW guild isn’t of any interest for my wife. Worse, the more I talk about it, the more she resent it.
Or
This project I want to discuss only with my closest family doesn’t concern any of my friends, even less my so called-facebook-friends.

There are a few initiative in this direction. HonestyBox is a great Facebook App, it brings something really missing.
You can send a message anonymously. At last, you can be something else than just polite or nice.
There are also private social networks or VIP-only social networks.
ModelsHotel is one of them. As Michael Arrington said: If You’re Not A Model, Don’t Bother Reading This.
So where is the solution ?
You can have as many social account as personalities. This can become hard to track…
You can try and set a really complex permission/privacy panel on the one and only network you choose (if it has this kind of option, today, I don’t know any that has).
Clearly these are not real options.
That leaves room for innovation…

[update 2008-02-27]: Seth Godin said it with his words (yes, they are better than mines. He is the marketing guru. Not me…).