There's also a nice write up by a networking adminstrator (I haven't the bookmark anymore), where he talks about the origins of TCP, and how it expanded to IPv4 and then carries on to discuss IPv6.
It points out some interesting statistics concerning the available amount of IP addresses.
Apparently, four billion is the max via the IPv4 technology, and currently we have used/reserved upwards of 2.5 billion. We also consume/reserve about 200 million addresses per year. Simple math would suggest that by 2015, there will be none left. The question of claiming back previously owned addresses is valid, but a convulted process, as there's no law that would require people/companies to have to relinquish ownership.
Fortunatley IPv6 is built with a different format, so that every person living now, and born, until the sun explodes, would be able to own fifty of their own addresses. Hence, we'd never run out so to speak.
While IPv6 was introduced over ten years ago, and it is used, the cross over isn't quite so simple.
It will be neat to see how these two issues tie-in together.