Digg was great for bloggers around 2005. I created software to add hundreds of friends per day (I think the limit was 250..and the only way to do efficiently was with software).
I only had to post a link a few times a week and the friends on my list would up vote it automatically (I never had to ask them). This would hit critical mass at about 20 Diggs and I would get to the front page.
Front page at that time would get me about 50,000 unique visitors and a good percentage of other blogs picking up my articles and coming back regularly. The trick was to write good content, not just top 10 lists.
I was just a student at that time and didn't have much business experience, but I was able to sell some custom PHP scripts. I think I made about $1000/month for an entire year.
Eventually they cracked down on it, and I got a job and stopped updating my blog.
I wish I would have been able to capitalize on it a lot more. I probably could have turned it into a much longer-lasting business.