It would be interesting to create a social network that used a constraint like personal space to determine what rank they were.  I wanted to create one a while ago that was all about who you've taken to the airport or helped move, as those are two activities that restrict your friend group to a pretty limited set.  Unlike myspace or LJ, you can't just add everyone as friends... unless you have taken everyone to the airport and helped everyone move.  But, this game sort of makes me a jerk because I don't have a car so most of my relationships seem to be one-sided.

But personal space is a little fairer.  There are 5 zones of space according to this book I'm reading on body language:

1. Public Zone: This space doesn't belong to you at all, and it's where any old stranger can be without you feeling threatened.  On average, it's about 12 feet away from you.
2. The Social Zone: Somewhere between 4 and 12 feet, this space is for people that we could potentially interact with.  Plumbers working on our sink, waiters, etc.
3. The Personal Zone: Between 1.5 and 4 feet, this is for friends, coworkers, family, and people you trust.
4. The Intimate Zone: Between 6 and 18 inches.  This is the one that feels the most wrong when violated.  This is your space, and is reserved only for people who are emotionally close to you.  There's a sub-zone called the Close Intimate Zone which is even more restrictive and is 0-6 inches... which is used as you might expect.

I think that the distances here are, strangely, for faces.  People can come closer to their allowed zone as long as their faces stay the right distance away.  Haha.  Do you think that's true?

People who enter the Intimate Zone without permission are interpreted as intruders and possible attackers.  You have physical reactions to that violation, like increased heart rate, adrenaline, etc.  Strange that we have all these rules about space... the more I think about them the more complicated it all is.  Just think about how you react to each gender differently, and to people who are higher or lower on the status totem pole to you.  And what different social situations do to change the personal space math (like elevators, movie theaters, buses, airplanes, concerts, etc). 

So, maybe on Facebook or myspace or LJ we should say how close we've been to each of the people on our list.  It would be funny.  And possibly scary.  Maybe it's too much information.  But at the very least it would allow you to create a tiered set of friends that was somewhat objective and accurate to some strange formula in our heads.