They say that the source URL (i.e. the URL of your web link or web page which was just Dugg) is specified as the preferred version of the URL to search engines and a meta noindex tag is used to keep DiggBar pages out of search indexes. DiggBar basically builds a new page with a few new tags included atop it in the source code so that your search engine traffic juice and search engine ranking credits go only to your website rather than the Digg shortened link.
On checking the DiggBar enabled webpage's source code we found the following interesting facts:
º A link rel="canonical" tag is included in <head> to indicate that the original URL is the real (canonical) version.
º A meta noindex tag is used to keep DiggBar pages of your webpage out of search indexes.
Thus you should stop worrying about the DiggBar and use it's good features as a URL shortener and many others to make your work even more simpler.