As can be read on http://about.digg.com/faq it is impossible to automatically delete your account. You should ask them using the webform named on this page.
URLS:
http://www.digg.com
http://about.digg.com/contact
Please note that AccountKiller.com is not associated with the business listed on this page. AccountKiller provides easy-to-understand instructions and guides on how to cancel charges and relationships from the list of businesses on our site, we have no affiliation with these businesses.