Script Summary: Adds Reddit comments to Digg for the same article & allows you to submit comments to Reddit as well.
One limitation with this script is that it won't be able to find the same story on reddit if the URL is slighty different. e.g. digg story link - http://www.foo.com/index.html reddit story link - http://www.foo.com/index.html#article
Here are some articles that you can test the script on that have comments from both sites.