Hi Justin,
That makes sense - the duplicate content issue is one I'm assessing on the site at the moment as a result of our use of an SSL cert. We have our homepage under a SSL (https://) and other content on the site is on a regular http://. As a result, I think we may be suffering from some duplicate content in relation to this - when you click on a tier 2 page link from our homepage there is a 302 redirect that brings you from https://domain.com/page2 to http://domain.com/page2.
All stuff that I thought would have been address during development, but the SEO beast needs a lot more attention than initially thought!
Thanks for the help though, and the SEOMoz community have been really great in answering a number of questions so far. Lots of great info.
Cheers.