On 6/8/2011, several companies and websites are testing the new IPv6-adress-standard.
The old standard IPv4 has to be replaced, as there are no more free slots.
Sites like Google, Facebook and Yahoo! are joining this test.
Learn more about this day on the site of the ISOC (Internet Society).
There is also a little Test-Site to check if you will be running into problems with your current configuration.
Here you will find the wikipages of IPv4 and IPv6: