Often they can give you great increase when story appear on front page, but it doesn't mean that site will increase in future.
often it is like this:
day 1: 100 people
day 2: 97 people
day 3: 34 056 people (Digg homepage)
day 4: 967 people (Digg 2-3 page)
day 5: 403 people ( people still clicks their Digg profile saved links)
day 6: 100 people
day 7: 102 people
day 8: 95 people etc...
Your traffic stay the same.
Find answer here.
http://images.google.com/images?um=1...q=digg+traffic