I did a quick search for this and I didn't see anything on AO... so check this out!!!

Taken from www.slashdot.org
Remotely Counting Machines Behind A NAT Box
Posted by timothy on Wednesday February 05, @04:40PM
from the you-knew-this-was-coming dept.
Overtone writes "Steve Bellovin of AT&T Labs Research has published a paper showing how to remotely count the number of machines hiding behind a NAT box (in IMW 2002, the Second Internet Measurement Workshop ). Your friendly DSL or cable broadband provider could implement this technique to enforce their single-machine license clause. Bellovin explains how to change the NAT software to defeat the measurement scheme, but the fix is complicated and unlikely to appear in commercial home gateways anytime soon."
The PDF is here.

It def. makes for some interesting reading. This could be some very bad news.

I would consider this a invasion of privacy. It is my business how I use the bandwith that I "rent".
Who is to say that I only have one PC that has web access and the rest are for other purposes? What a crock of you know what!

This also has a negative impact on network security too.
This technique can make it easier for an attacker to enumerate your network... amongst other things.