I've been concerned for a little while now with WordPress's default functionality of creating duplicate content.  Each post is located at its permalink (/2007/03/01/post-title/), its date (/2007/, /2007/03/, /2007/03/01/), its category (/topic/wordpress/), and its page with respect to the homepage (/page/3/).  This might be a good thing, but to me it seems like it makes things more difficult.  If somebody finds my site through a search engine, they might be directed to an old location that no longer has what they were looking for.  For example, if something like /topic/wordpress/page/2/ came up in Google's search results, it might contain old data seeing that the second page of the WordPress category will inevitably change over time (since everything is sorted in reverse chronological order).  The post you're currently reading will eventually move from the first page of the WordPress category, and it'll eventually continue to move on from there as I put new posts in the category. 

The solution to this is with a simple plugin called Wordpress Duplicate Content Cure.  If the current item that's requested is a single post, a page, or the home page and it's not paged (i.e. /page/3/), the plugin tells search engine robots to index it.  If any of those conditions aren't met, it tells the robots to not index it.  Simple as that. 

We'll see how this works out in a few weeks or months.  If it has any negative affect on my Page Rank, I'll go back to the old way.