I just read this on the wiki, when Googling for a general piece of information about IPv6:
“While IPv6 is supported on all major operating systems in use in commercial, business, and home consumer environments,[3] IPv6 does not implement interoperability features with IPv4, and creates essentially a parallel, independent network. Exchanging traffic between the two networks requires special translator gateways, but modern computer operating systems implement dual-protocol software for transparent access to both networks either natively or using ‘tunneling’ such as 6to4, 6in4 or Teredo. In December 2010, despite marking its 12th anniversary as a Standards Track protocol, IPv6 was only in its infancy in terms of general worldwide deployment. A 2008 study[4] by Google Inc. indicated that penetration was still less than one percent of Internet-enabled hosts in any country at that time.”
12 years, and <1% deployment! This is what happens when you don't have a good transition plan from one technology to the next-- no one adopts it... I personally think it's likely 12 years from now, IPv6 still won't be the 'standard' used for the Internet... Many IPv6 proponents claim IPv4 is "end of life", as the IANA just assigned the last big /8 net block-- claiming "all the address are used up!" What they fail to understand, is that addresses aren't consumed-- they can be re-used, and they're allocated by the IANA in huge blocks, and all those organizations that they allocate to, then sub-allocate to other organizations that allocate to end users.