I'm sure by now I come across as obsessed by Twitter, and maybe that's not an unfair assessment. It's a unique tool that allows extremely easy discovery of "interesting people," and allows you to engage in fairly intimate interaction with those people.
Scoble has huffed and puffed and blown the house down over his "you are who you follow" assessment, which, to me, reeks of grade school cliquey-ness. Why does it matter who I follow? Why does it matter who you follow? Use Twitter however it suits you.
However, there IS one metric I would like to see: on average, how many people do the people who follow me, follow? With what kind of standard deviation, what's the mode? I think that would give you a fairly objective measure of the value of your contribution to Twitter, by gaging the selectivity of those who select you.
Does that make me hypocritical in my use of Twitter? I "follow" over 1300 people, and am "followed" by something like 1400. I certainly follow some very interesting, delightful, informative folks. There are definitely a number of people I interact with regularly. At the same time, there's no question, I follow some people who contribute little or nothing to my life most of the time. People with whom I've never had a conversation. People whose tweets have never twinked my noggin'.
There's definitely an imbalance of value in Twitter. Call it the Great Friend Divide, a la Scoble, if you will. I personally feel that I get more value out of interacting with a large number of interesting, intelligent people through Twitter. However, for every additional person I follow, that's additional segmentation in the attention I pay to my Twitternet -- any one node on my net tends to get less attention.
In other words, there's more value in being followed by someone who follows fewer people, than someone who follows a lot of people. Once you reach a certain point, the only way to get a message through to you is with @s or direct messaging -- which is where Twitter becomes transient, and loses a lot of its initial intimacy potential.
I suppose it all depends on how you use it, what you expect out of it, and what the people who follow you expect out of you. Maybe that's what makes Twitter great.