Here are a collection of interesting sites to visit on World IPv6 Day
The World IPv6 Day "Eye Chart" causes your browser to visit a number of prominent IPv6 Capable sites:
http://ipv6eyechart.ripe.net/
IPv6 Day Survey - test of dozens of IPv6 capable sites for differemt protocols (HTTP, SMTP, XMPP, etc)
http://www.mrp.net/IPv6Day.html
Akamai Real Time Statistics:
http://www.akamai.com/ipv6
World IPv6 Day participant site status:
http://www.worldipv6day.org/participants-dashboard/
RIPE Network Information Center Dashboard, including AAAA record visibility:
http://v6day.ripe.net/
Path MTU analysis and research:
http://hide.dnsalias.net/aaaa/worldipv6day.cgi
Feel free to tell us about more in the comments!!
