How much is a customer worth?

Vonage IPO raised a few eyebrows with its value per subscriber, and it got me thinking about how we value our customers.
It occurred to me that telcos really only know 3 things about their customers (if they're lucky); their name, their address and their ARPU. They know some other stuff that confirms identity and they may know a bank account number, but essentially a customer is packaged in a little box that says "J. Public, $25/month, credit rating: Good".
This tells me very little about the customers potential, or why they are my customer, or how 'sticky' they are likely to be. What are the things that concern them, what do they do, who do they call?
Ok, we're getting into a grey area here where the telcos could get a lot of statistics together and mathematically calculate some reasonable answers from their data; I'm just not sure they would ask the right questions...

Vonage has 1.6 million subscribers that it knows very little about. Each of those subscribers was valued at around $1600, based on growth potential. For what? More VoIP?
Let me take another company with a growing customer base, significantly lower revenues, but, imho, with a far higher customer value. LinkedIn
The reason the value is higher is because there is community and trust built into the system.
When I first signed up for Linkedin back in 2003, or thereabouts, I was excited at its potential as a directory service, rather than the recruitmentfest that it has become.
Combine LinkedIn with Iotum and you would have a pretty powerful way of screening calls, without much in the way of 'relevance' logic.

But LinkedIn is failing to see that its growth is hurting its value. The value of their customers is being diluted as their service expands.
Why? Because of Ron Bates! Now Ron might be a nice guy, but he is one prolific example of the disease affecting social networking sites. Ron has OVER 25,000 connections. I can connect to hundreds of thousands of people, but that name always pops up! He breaks the trusted network. I would remove him from my list, but in LinkedIn that is not an easy thing to do, and perhaps he wouldn't like it and bring all his 25,000+++ buddies down on my profile, changing my name to Mud!

In calculating the worth of a customer, the links we have in the social network have value, but that value is not uniform. The social networks, like MSN, Yahoo, Skype, AIM etc MUST allow us to reflect the value of our connections within the social fabric. If they don't, they will be compared with the shoebox telcos like Vonage and they will miss out on a whole lot of opportunity.

It's not what you know, it's who you know that counts...