In his recent and excellent book, Linked, Albert-Laszlo Barabasi describes in detail "scale-free" networks. Everything from the internet, to the 6 degrees of Kevin Bacon follows the laws of this network, which unlike Poisson distributions, match exactly the distribution of nodes on the internet...as well as the Al Queda network. Well, one of the key points he makes is that there is inherent reliability and vulnerability in such networks. The reliability comes from the numerous routes that traffic can take. The vulnerability comes from the fact that there are "super nodes" that carry a dissproportionate amount of traffic. If you have not read about the UUNET router table failure yet, this shows the vulnerability aspect well.