I just realized a mistake I have been making with social bookmarking sites. I thought that bookmarking was just for the few clicks you get from posting there. It is like watching traffic from a window, you only have a few chances for people to see you. Caroline Middlebrook pointed out that link goodness can be found from these sites. BUT they have to be Dofollow bookmarking sites:
So she has kindly listed the dofollow social bookmarking sites that you need to get your posts onto.
I suggest you read carefully her numerous posts on social bookmarking. It will give you a good perspective on this area of traffic growth.