I have submitted a few (very few, unfortunately) articles to some article sites. For the most part they do work. I see visitors from those articles on a regular basis. I do believe that if I had 100 times the articles in the directories that I would see approximately 100 times the visitors from these sources.
Of the articles that I have posted only one has not performed. This article is posted with EZine Articles. It is not for lack of views of the article that it has not performed. EZine has good analytics in place and I can see that the article is being viewed.
I suspect that the primary problem with the article is the call to action in the resource box. An other article that has had a similar number of views has a 16% click through rate while the article in question has had no click throughs. Perhaps it is the content or the category under which it is listed, but I think that the problem is that the resource box is not compelling.
The articles that have performed best for me have been on EZine Articles and Buzzle, the sites that have the highest standards. Because of their high standards the backlinks from these sites may carry more weight. That may help to improve your SERP, and along with good key words may get you to the front page of the search results.
Article marketing can be a good source of ‘free’ traffic. Present good information with a good headline and the material will be read. Pay particular attention to the call to action in the resource box and you will see some traffic to your site. It does take some time, but it can be a great benefit to your and your site.