What the heck is World IPv6 Day and why should I care, you ask?
In short, IPv4 was the most recent manner of providing IP (Internet Protocol) addresses for all sites on the Internet. While it is easier for humans to remember names like Amazon or Google, computers need numbers and so each "named" site is quickly converted from text to binary (1 or 0) so that your computer takes you to the right spot on the net. Because IPv4 is comprised of 4 sets of numbers there were 232 or 4,294,967,296 IP addresses available for use, but they are running out. Enter IPv6 with its 264 possibilities and a whole host of new IP addresses.
Why should you care? Honestly, it is not really an issue for most people. If you have Vista or 7, you should already be set for IPv6. If not, it might take a bit of configuration to get ready. If you want to check your readiness, head to the IPv6 Eye Chart and find out!