OK, there are some good questions here.
Let me make it clear at the outset that I agree that it is possible to do well with MANUAL article submission. One of my mentors, Cynthia Minnaar, has achieved excellent results with this method.
Personally, though, I use SubmitYourArticle.com which gets my articles submitted to ezinearticles and a lot of other good quality directories.
SYA also has a feature that addresses the "duplicate content" question. When you write an article, you have the option of making alternative versions of the title, the opening paragraph, ten or more sentences in the main body, plus as many different versions of your signature file as you like.
SYA then sends out a random combination of alternatives so each directory receives a different version of the original article.
Also, the articles can be "trickled" out over a period of several days rather than all going out together.
So, if you want to submit to 100 directories, doing it this way is a huge time saver. It is all about efficiency and productivity.
