Let's say you search for microsoft.com on Google. You'll then be shown the usual:
Show Google's cache of www.microsoft.com Find web pages that are similar to www.microsoft.com Find web pages that link to www.microsoft.com Find web pages from the site www.microsoft.com Find web pages that contain the term "www.microsoft.com"
Now, when you I click on the "link to", rather than seeing "link:" info, I see randomly assigned strings before eg. "Results 1 - 10 of about 129,000 linking to VRA9OSkpgNsJ:www.microsoft.com/"
... and by chance all the cache links for documents that I have viewed in recent days are now light blue again: that either means that they dropped off the end of my stored history (unlikely, the history is set for 10 days), or more I believe that the actual DocId has changed for those pages, even though many are showing a cache date dated from 5 to 15 days ago.