can digg links helpful

That's good news.

I have heard many social bookmarking sites help in building backlinks.

Yes. Social bookmarking sites help increase backlinks as long as they use dofollow tag.

Submitting to dofollow social bookmarking sites helps in building links and it also helps in bringing traffic to your sites.

Yes. If the link is dofollow it will be counted as a backlink.

Links in dofollow sites is always helpful for PR cos is additional backlink but most of the social sites uses no follow attributes.

In terms of acquiring traffic from social sites they can suddenly boom out if the submitted story is interesting...but not that much to rely on..

I believe the benefits of digg are more in the way of traffic, if the story you are digging is on your site and it gets large amount of diggs then you will see a lot of unique traffic.

The problem with digg is you get traffic but very rarely visitors come back.

i been using digg to get link backs, it works and helps get new sites in the search engines.