http://www.Stumblexchange.com/ and its affiliates. A bunch of DPers use them and get relatively decent results (~100's of hits per day). You could also buy links, which is a much more targeted way of promoting it. Anita
There are much more better social networking sites other than digg. Search around the forum and you should be able to find a list.
Be carefull -- if you are telling DP forum members or may be other forums to digg... Digg can track those clicks coming from DP and you may get banned.
Stuffed? What do you mean by stuffed ? Yourself digging each and every article on your site WOULD definitely get you banned, even if it's unique content. This is ok with me. Other people should submit to Digg, not yourself million times a day.
Except you only get one ad click for about every 500 people. It's good at traffice if you get popular, but even then it's not effective traffic.
It probably depends on the site. In my case I do better with newsvine. I dont get as much traffic, but the traffic that does come is usually better quality. But really, I wouldn't recommend social networks in general as the main marketing. It's ok for added traffic, and the price is right, but I'd rather throw some money at local radio or other traditional media.