Using article sites is generally considered to do several things: -Providing a sense of authority on whichever subject that you are providing content on.
This can serve to really build confidence in your product or services that you are providing.
This can mean significant reduction in the time that you need to spend on building that trust in the relationship between your site and its visitors.
-Most article sites will let you add a link back to your site, from their perspective you are adding additional content to their site, and this also serves to carry further authority in terms of the anchor text that is included in the link which can serve to improve the way this is perceived from the search engine spiders.
The higher quality article sites such as EzineArticles will generally check the content which you place on their site to ensure that it is unique.
However, some of the less scrupulous sites do not offer such a service.
Therefore I have heard it suggested that if you submit your content to the higher quality sites first then the lower quality article sites then this can mean that you can generate significant numbers of links.
Use a ping service to ping the articles once they have been submitted can mean that they are indexed quickly.
If you are placing lots of links, it is important to ping each of them several times as this can ensure that your links get noticed.
Once you have the articles approved using a social bookmarking system can the prove to provide additional sources of traffic to the article, which in turn should then generate further clicks to your site if the article is structured correctly.
Most article sites have specific rules in terms of the number of links that can be included in the text of the article and personally I am of the opinion that you should only include a maximum of one link in the main text of the article with an additional link in the author bio at the bottom.
Then if someone wants to use the article on their site they are more likely to include it than if there are 3 or 4 links.
If someone does choose to publish your article, this then serves to further spread your links around the internet without you having to do anything.
This does not happen all the time, but can serve to massively increase the levels of traffic to your content when it does occur.
So in summary, placing articles on article sites does definitely need to be included in any link building strategy, as long as the content is strong there is no reason why this will not help your links and also the traffic to your site.
However, personally I would use article marketing as part of a wider link building strategy.