http://www.google.com/intl/en/ipv6/index.html
http://www.google.com/intl/en/ipv6/statistics.html
http://www.google.com/intl/en/ipv6/faq.html
What are IPv4 and IPv6?
IPv4 is the current version of the Internet Protocol, the identification system the Internet uses to send information between devices. This system assigns a series of four numbers (each ranging from 0 to 255) to each device. IPv4 only allows for about 4 billion addresses and the Internet needs more room than that. IPv6 is the new version of the Internet Protocol and expands the number of available addresses to a virtually limitless amount–340 trillion trillion trillion addresses.
Why is IPv6 important?
The Internet is running out of IPv4 addresses. Transitioning to IPv6 enables the Internet to continue to grow and enables new, innovative services to be developed because more devices can connect to the Internet.
