Depends on the time of day and the amount of Diggs your post gets. I've had one post hit and gain upwards of 650 diggs (http://blog.jakerocheleau.com/2009/...s-starting-out-in-website-design-development/). My traffic got a large spike of about 8k uniques that day, but that wasn't from only digg it was also from it hitting on Delicious and StumbleUpon, too. Digg sent about 6,500 uniques that day. My second article was actually an interview with a software engineer from digg (http://www.insidethewebb.com/2009/11/interview-with-a-digg-com-software-engineer-kurt-wilms/) which got about 350 diggs. This only brought me about 5,000 visitors that day, but it's slowly been bringing in traffic not only from digg but also Google and Yahoo! Hitting digg won't make your blog the #1 blog all of a sudden, you still need to grind with your marketing even if you do end up on Digg's front page. But I will say once you see your article has been promoted to the front, it's a really good feeling to know you did it
You need to have superfast server and got to use some kinda social book marking or article submission tools that can post things in bulk. Still we can not assure the required output.