Not once they start using the "rankings" of each person and using them as a portion of their site ranking algo...
You know there IS a purpose to sites like DIGG, StumbleUpon, etc... besides spamming your websites for promo. Hundreds of thousands of people actively participate because... they like to. Yahoo Buzz? Same deal...
It would be a funny day in Google Land if they DID incorporate this into all SERPs... and everyone voted all the Wikipedia articles to the top.... which, honestly, could happen.