Digg is a site where users can submit news stories that other users can vote up or down. The stories with the highest votes get pushed to the front page of the site. Because stories had no be manually submitted, it cut down on the power of major publishers. In a world before Twitter and excessive Facebook status news sharing (2004), this was the best way to get a sense of the news that people found important. So why don't I use it anymore?
I no longer use Digg because it has become a bloated mess after Digg's latest revision last year. What was once a front page driven by users (though some did admittedly game the system, like Mr. Babyman) became a dominated by major news publishers who were allowed to automatically submit content to the site. Digg became one huge RSS reader - one that purported to be the view of the community. Meanwhile, sharing news links via Twitter and Facebook became the new social currency.I can safely says that I find out about breaking news (like today's acquisition of T-Mobile USA by AT&T) from one of these means quickly.
Digg fell behind the times. Since Digg's founder Kevin Rose resigned in the last few days, there has been a flood of news coverage on Digg. In particular, Sara Lacy wrote a great Techcrunch piece on what Digg meant to the San Francisco tech community. It's a shame to see Digg fall apart in shambles and die as a former shell of itself, but that's what happens if you don't continue to evolve your product with the market.