Just what is digg? According to their website, digg is:

a technology news website that gives editorial control back to the community. Most technology websites allow users to suggest content by submitting links or stories to an editor. If the editor believes the story to be relevant to the masses, he or she moves the story to the homepage. With digg, users also submit links for review. But rather than allowing an editor to decide which links go on the homepage, the users do.

Essentially, stories are moved to the digg homepage based on the number of users who find the story useful/interesting as well as the history of the users who are digging the stories. Their FAQ offers a more in depth explanation. The part of digg that I found interesting was the interaction possible between users. digg.com has RSS feeds abound, allowing users to subscribe to specific sections, or even to specific users, letting you keep up with what friends or users with the same interests are digging throughout the day.