The Internet Archive announces the Wayback Machine. Enter any URL and see what they have archived and when, then view it, in real time. This is an invaluable tool for archivists and researchers. It will almost certainly blow out copyright issues to the fore, as it has before. F'r'instance.
It just hit me that this could be a national security problem. Nuclear plants are revising their sites to move previously quite explicit information about the site location, such as maps. But then, you can use the Internet Archive to view Hanford Nuclear Reservation in the past.