does it work to promote a page on digg like sites?

As for my experience, Digg really helps somehow for backlinks but a little on traffic. But, I still like Digg. :)

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.

Digg generally eats your bandwidth and creates a "slashdot effect" which denies service to your site. However, it can yield some good traffic and backlinks.

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?

I think there must be a better way to spend your time. That would be a real headache to try and handle 50 fake accounts.

plus its probably illegal

Digg will help you in getting traffic but it's not advisable to use multiple accounts.

Digg is dominated by some of the prominent users and tech community those having good hold, don't expect much from digg.