On June 8, Microsoft will enable world-wide IPv6 connectivity to Bing.com, for the purposes of a one-day test. Consumers with IPv6 Internet capabilities will automatically access this new method of connectivity. This necessitates both a device that supports IPv6 (like a Windows 7 PC), and support from your Internet provider.
IPv4 traffic will continue to connect to Bing without any change. In fact, most Bing users won’t even notice that this transition is occurring.
Souce: Bing Blog
For a list of the current participans in the World IPv6 Day visit http://isoc.org/wp/worldipv6day/participants/