Nothing, they say. According to this forum post, they have plenty of IP addresses in the IPv4 world, and if you, the end user go IPv6 now, you won't be able to connect to everything out there on the Web:
We're not currently planning to convert to IPv6 anytime in the immediate future. The whole point of demand for IPv6 is that "IPv4 addresses are running out" (a very valid problem if you live in Asia or Europe), but we've already obtained a large stockpile of IPv4 addresses so we're not concerned about such.
Do bear in mind that although IPv6 Launch Day was yesterday... most of the internet ISN'T accessible if you're using IPv6. In fact, only about 30% of internet pageviews are possible if you're using IPv6; the remaining 70% of the time, you're trying to access a website that doesn't have IPv6 enabled, which means you're out of luck unless you have an IPv4 address. (»blogs.cisco.com/news/ipv6webimpact/)
Of course, the internet is hardly static, and as things change we may later decide to convert to IPv6 if that's the best thing for our users. Right now, however, the best service we can provide means sticking with the more universally-accepted IPv4 standard.
That throws a little cold water on the whole IPv6 thing, don't you think?
So how do web sites cope with this? Steven J. Vaughn-Nichols looks at the issue and sees that even though IPv6 traffic is only 1 percent of total Internet traffic, big sites are looking into and implementing a "dual-stack network solution."
SJVN sums up:
While IPv6 may still be a trickle today, it’s soon going to be a flood, and the sooner you start making the change the better.
Remember, we really are almost out of IPv4 addresses, and by 2013, most new internet services and websites in Asia, Europe and North America will be only reachable by IPv6.