Like Jaan said, the link and visitors from Digg and other social network sites is more or less inconsequential. The real juice from those sites comes from the links you will get from blogs and other sites that picked up your story on Digg. mtb167 said that you can get 300-800 links from a front page Digg story and according to Neil Patel this is a low estimate. At SES NY this year he said he averages thousands of links from front page Digg stories.
Getting content on sites like Digg can provide a huge boost on link popularity and that is the real
SEO benefit from social network sites. Just be careful to avoid too much self promotion because the users there can spot it pretty well and they will bury you as fast as they can if they catch you doing it.