June 8th 2011 (00:00 - 23:59 GMT) is World IPv6 day, when a number of large internet organisations such as Google, Facebook et al are enabling IPv6 for the next 24 hours. With widespread testing tools available ahead of the event, the expectation is that few users, if any, should experience connectivity problems today.
Whilst Google has operated an IPv6 network for some time (on ipv6.google.com), this will make IPv6 addresses resolve for the main www.google.com address as well:
$ host www.google.com www.google.com is an alias for www.l.google.com. www.l.google.com has address 209.85.143.99 www.l.google.com has address 209.85.143.104 www.l.google.com has IPv6 address 2a00:1450:400b:c00::63 $ host www.facebook.com www.facebook.com has address 66.220.146.25 www.facebook.com has IPv6 address 2620:0:1c18:0:face:b00c:: $ host www.bing.com www.bing.com is an alias for ipv6.search.ms.com.edgesuite.net. ipv6.search.ms.com.edgesuite.net is an alias for a1877.dscb.akamai.net. a1877.dscb.akamai.net has address 82.71.193.234 a1877.dscb.akamai.net has address 82.71.193.241 a1877.dscb.akamai.net has IPv6 address 2a02:26f0:24::5c7b:9a5b a1877.dscb.akamai.net has IPv6 address 2a02:26f0:24::5c7b:9a42 $ host www.youtube.com www.youtube.com is an alias for youtube-ui.l.google.com. ... youtube-ui.l.google.com has IPv6 address 2a00:1450:8002::be $ host mail.google.com mail.google.com is an alias for googlemail.l.google.com. ... googlemail.l.google.com has IPv6 address 2a00:1450:400c:c01::53
If you have an IPv6 connection, or you are using a tunnel from providers such as Sixxs.net or He.net, then when you visit these sites you will automatically use the IPv6 versions of these sites.
With the final IPv4 blocks having already been allocated, moving over to IPv6 is an essential step in the continuation of the internet's growth throughout the globe. But like the chicken-and-egg scenario, without IPv6 hosts to visit, there seems little advantage in clients having IPv6 connectivity.
The tide is turning though, with many Asian countries aggressively rolling out IPv6 servers and clients. If World IPv6 day is a success, then it may well be that the servers keep the IPv6 enabled from now onwards.