All the social networks are a great way of getting your site seen.. Not only do they get website more traffic but they also get backlinks when people write about one of the submitted posts in there… And Digg really only works well if you have friends within the Digg community and even still, not all your friends will see your submissions and even if they do, they might not vote.
I was rather thinking about using pages like upcoming.pl where only 5 votes are enought to get on front page. digg need around 250 votes and it's imposible to fake it. But creating 50 fake accounts on 10 sites take a lot of time . I wounder if it's worth it?