We are a little early for IPv6 day, but www.cpan.org has since a few minutes ago gained AAAA records. This means that if your system has an IPv6 address, it will likely access that CPAN mirror over IPv6. Woo!
It also means that if your system thinks it has IPv6 access, but doesn't really – it'll connect much slower.
Our friends at Dynect monitors the IPv4 addresses for a couple of mirrors in California and one in Europe and makes sure that www.cpan.org is always accessible. They don't offer this service for IPv6 yet, so for now IPv6 just gets round-robin DNS for two of the mirrors.