Luke,
at this moment a new website is developed for me using Modx CMS. In here I had build a blog because I want to start blogging too. The funny part of it is that in many cases blog software creates duplicate content if you post an article and also have it stored in the archives etc. Modx does not seem to be doing that (so far as I tested it).
Maybe that would be something too look into?
The archives should be linking to the same article as the overview page does. The more tags and the more categories helps the user define what they are looking for and that ought to be a good thing. Here in the SEOmoz community you can also filter out certain blog messages, for instance if you only want to see white-board Friday messages that's possible. And I believe that these do not result in duplicate content issues.
Hope this helps you
Regards
Jarno