Two days ago Loren Baker wrote Does Digg.com Belong in Google Results? He basically summarized two points of view, the first by Allen Stern who says that Digg adds no value to the story and should not be indexed (hence duplicate content). The second point was by William Burn, who argues that Digg's pages do provide value and give pages that may have never been read a chance. Skizzo adds that he doesn't like when commentators copy and paste the original content from the main site in the comments of the Digg post.
OK, having read all that. I also would like to see the original article found first in the Google results. I do believe that the Digg article should be indexed and found. Typically, a Digg title may differ from the original article's title and thus has doubled its chances of coming up in the results. If you are worried about article hi-jacking, then that is a different story - but I would say, just go with the flow.
As an SEM, I can understand why you don't want to be outranked by a commentary to your article. But often, commentary to one's article does provide greater value. Often, but not always - I must add. If the Digg article does add value and that value is greater then the original source, then it should outrank the source article.
Either way, people are reading your thoughts and you got a nice link from Digg. The value of the link from Digg, is discussed here.