The image, from one year traffic trend, shows Digg nearing Slashdot traffic levels after less than a year after launch. Slashdot is red, Digg is blue.
Digg allows anyone to submit news stories, and other users vote on how important the news is. More popular stuff moves to the top of the site, eventually gaining front page promotion.
It thas recently raised funding and saw traffic spike even more as publicity about the site spread from hard core net news junkies to mainstream internet users.