Hi Taggart,
Welcome to the Forum. Thanks for joining our community.
There are various tools that help you to identify duplicated content on your site:
www.virante.com/seo-tools/duplicate-content.php
This tool will look at:
* www and non-www header response;
* Google cache check;
* Similarity check;
* Default page check;
* 404 header response;
* PageRank dispersion check (i.e. if www and non-www versions have different PR).
www.google.com/webmasters/tools/ will help you identify duplicated titles and metadescriptions.
However, you don't have to worry about duplicated content on your site. Matt Cutts, Google's 'anti-spam Czar' lays fears about this to rest here:
www.mattcutts.com/blog/duplicate-content-question/
Cutts says:
typically a whitehat site doesn’t neet to worry about 1-3 versions of an article on their own site.
He does warn about duplicated content that occurs offsite. This can be created via syndication:
However, I would be mindful that taking all your articles and submitting them for syndication all over the place can make it more difficult to determine how much the site wrote its own content vs. just used syndicated content. My advice would be 1) to avoid over-syndicating the articles that you write, and 2) if you do syndicate content, make sure that you include a link to the original content.
Of course, another thing to worry about is that people would be stealing your content. A service like:
www.copyscape.com/
can help you find duplicated content. Usually writing a legal letter to the website owner gets the content removed.