I doubt they are:<p>1) the volume of popular stories on digg/reddit/stumbleupon/hn etc cover a miniscule portion of the internet and aren't necessarily more important or better than the overwhelming majority of the internet.<p>2) Google can't trust votes/users, and in lots of cases can't even see who made the vote let alone decide whether user x on site y is legitimate. They also can't trust the sites to handle that themselves - they get gamed all day every day with fake accounts/paid submitters (even on HN!), manufactured content, summary spam etc.<p>3) every site implements/displays it differently which would mean scraping most of the time, and tapping into APIs only some of the time.<p>There are SEO benefits though like people linking to your site because of the popular submission, your site spending a day or two on a high-PR website's front page etc.
Short answer: No, but many search engines are increasingly aware of the microformat data you may wish to supply. (<a href="http://www.google.com/help/features.html" rel="nofollow">http://www.google.com/help/features.html</a> of some examples)<p>This info shows up when you search for things like movies and Google shows "3 1/2 stars" or "starts 7:30pm." I forget the format's exact name but there's a lot you can provide.