Just go to Digg and find out... http://digg.com/ It's a social news sharing site for popular news articles, blog posts, images, etc.
It is off course a Social site, it helps you to gain a good visibility. If you need a exposure you can opt for it
I like to think of it as a book club. People find stuff that they like on the internet and they are telling you they think its worth your time to take a look at it.
I guess that is one way of describing it... kind of weird to say a book club, but yeah I'll go with you. An internet web 2.0 book club
you can submit and vote stories. so you can see what people are interested in. and of course, discover new things. you should definitely try it. just look around and take some time. It's a great system. for social bookmarking you should use delicious.com...its better for such things
Digg is a social bookmarking site where people submit their links to get traffic and backlinks, social bookmarking sites have been prominent to build up your backlinks these days.