They get indexed, and when you search for backlinks to your site on Google digg links show up. I don't know how much weight they give, no one does. But definitely gotta be worth something for sure.
Digg has always been dofollow. If you reach the first page, you get huge traffic and some quality backlinks from other sites as well.
Google knows how much spam is dumped on digg. Though the site or page is indexed, it does not provide any value for search engine ranking. And I am sure, not in distant future, Google will start removing those spam sites from their index. If the site is not spam but provides values to users, it is always better to submit it to digg once. But submitting every page of a site to Digg is a sure sign of spamming.
Digg links will bring you traffic and will help indexing your site / pages faster. However I don't consider digg links as a quality link. Quality links are those from established sites in your niche with a limited number of outgoing links
hey no matter if they give link juice or not its better than noting. and i t definitely cant hurt you! digg away!
This feature of Digg has been very profitable for me. I've earned profits of around $10,000 from this in the past 5 months.