In our complexity group, Friam.org, we've been discussing whether or not there is an emergent property to Web 2.0. One contender is Reed's Law
Basically a component of Web 2.0 is migration from "Metcalfe's Law" and "Reed's Law". Metcalfe's law states the value of a network varies as the number of pair-wise connections between nodes, (the complete graph of the nodes). This varies as n^2.
Reed's law states the value of a network varies as the number of subgroups within that network. This varies as 2^n, a much, much larger number.
This transition is occurring due to the migration of the web from a publishing technology to a community.
A good article on the idea is "That Sneaky Exponential—Beyond Metcalfe's Law to the Power of Community Building"