In the words of Google there's no such thing as a "duplicate content penalty". Despite this people are still horribly confused about duplicate content. In a recent forum discussion a contributor advised others to amend their articles in order to avoid a duplicate content penalty when submitting to article sites. I disagree.
If you want to make use of article syndication sites, but you are worried submitting content to these sites may in some way disadvantage your own site, stop worrying. Once an original article is published on your site and has been indexed by Google, ie it shows up in a Google search, then Google understands that to be the original source of the article.
If you choose to share your content with a wider audience through syndication your own site will not be penalised.