There are a number of SEO advisors who recommend setting up multiple accounts with all the top social bookmarking sites, then posting links in each account to your own blog to drive search traffic. 

One place that strategy will backfire is at Digg.  Their terms of service limit each user to a single Digg account, and if you violate the policy they will ban you from their site (for life? hard to say).  You’ll get a message like “Due to the nature and severity of the abuse (i.e. setting up more than a single account) your account will not be reinstated.  This decision is final and irreversible.”

Hard to say if a Digg robot is the culprit for an impersonal message of that nature, but nevertheless they will stick to their guns.  Everyone knows the value of having your post make Page 1 at Digg, but just be sure you limit yourself to a single account when you sign up.