Today, big Internet portals are supposed to resolve to AAAA (IPv6) DNS queries in their main site. Thus, if your computer is enabled, it should try to access it using IPv6. It's also a good chance to see if AAAA responses to any machine (IPv6 or not) would cause any trouble in their OS or applications.

It's also some type of marketing to make the crowd aware about it. Many companies may have started on IPv6 because there was a day dedicated to test it.