From Telecomix Crypto Munitions Bureau
The main advantage of IPv6 is the vast range of addresses it provides. Every living person could be allocated an IPv6 block, each block being many times larger than the entire IPv4 address range. In fact, there could be billions upon billions of IPv6 addresses (actually around 3 x 10e25) for every square millimetre of the Earth's surface. This also means every single host connected to the Internet can be assigned a unique and permanent IPv6 address.
This new addressing system will, over the next decade, lead to a more decentralised Internet than the client/server model we're familiar with, where point-to-point communication between hosts is possible, and where content can be multicasted to whatever hosts are listening in on a particular address. IPv6 will also remove the need for Network Address Translation, leading to a more efficient system of routing Internet traffic.
 The Current Status of IPv6 Deployment
Although progress is slow, much work has gone into improving compatibility and the transition to IPv6. Most operating systems released over the past five years already support it. There is also a certification and IPv6 tunneling service being provided by Hurricane Electric.
The first large-scale test of IPv6 took place in mid-2011, where the major service providers enabled it alongside IPv4 using dual-stack and IP tunneling, and this proved the new system could be deployed with few problems. Another test could take place in 2012, and a permanent deployme 1da8 nt of IPv6 is possible.
 IPv6 and ARP
It seems the Address Resolution Protocol has been dropped from the IPv6 implementation to be replaced with something called the Neighbour Discovery Protocol, which helps local networks dynamically adapt as hosts are added and removed. Secure Network Discovery is also in development, which removes vulnerabilities associated with ARP.
 Multicasting and Anti-Censorship
A very useful, and possibly a censorship-defeating, feature of IPv6 is multicasting, which enables us to establish wide area mesh networks over the Internet by subscribing devices to particular 'channels'. IPsec might also enable secure messaging between a closed group of trusted devices.
- IPv6 routing in 3 minutes - the very basics