Well, if your already setup, then you wont have to worry too much. At the current rate, the general opinion is that new hosts will have to be assigned IPv6 addresses by 2012(if the world doesn’t end).
So if those hosts wish to communicate with the other IPv4 servers, using the IPv4 network infrastructure, hosts will have to start understanding both IPv4 and IPv6.
At least till the transition is complete. To make the transition as smooth as possible, various transition mechanisms have been put forward, of which RFC 4213(Basic Transition Mechanisms for IPv6 Hosts and Routers) will make an interesting read for any Webhost who plans to buy servers after 2012. More after the jump.