I ran a test at the beginning of 2006 till today on few articles: I wrote an article and posted on my site for few months, i waited it be index completely on all SE then submitted to few article directories just to see the reaction on google.
What happened eventually is that when i search a sentence from that article, I find few web site, but my original on my site is in the supplemental results.
My site is pretty strong and has the same page rank as the others on that SERP.
some of the site in the SERP don’t link back to my article or even mention my site it is easy for google to see that I’m am the original cause some other site on the SERP do mention my site ( not as a link unfortunately).
The google search is : "Despite its relatively tiny size, Manuel Antonio National " - Google Search
After the repeated My site is number #4

so from that poor experience (took me a year and half ) i have learned that i better keep the content on my site and not submit it. Wait till some site will pick it up and link back to the original.