I became aware of this because in the last few weeks I've had several stories that were pro-Linux and anti-Microsoft-Linux, it doesn't get any faster and Macs, Windows 7, and Linux--first became popular on Digg, and, an hour later they were buried.
On Digg, what this means is that, unless you already know the Digg link, or specifically search for a tale with the buried story option on, the story link disappears. In short, no matter how many people thought it was a good story, other people will no longer be able to see it.
Digg staffers explained that this happens because "The Digg.com community has collectively voted to bury the story to which you refer. Though the story has been buried, it is still available on Digg.com. If you or a friend Dugg, submitted or commented on the story, there will be a link on your respective profiles. If you did not have the chance to Digg the story, you can search for it at http://digg.com/search - just be sure to select 'Include Buried Stories' when you search."