People don't realize it, but WordPress publishes your content out through a number of paths when you have permalinks (highly recommended) turned on. You can get to your content by tag, by category, by archive, by page (next, previous), and usually by www.yoursite.com
and yoursite.com - etc., etc.
This actually hurts your ranking with search engines because people may be linking to the same exact content but from different URLs! That means that a post that you did that a lot of folks liked isn't getting all the credit it deserves. Recently, Google released a method for content management systems to handle this - called canonical URLs.
And of course, within hours a wordpress canonical URL plugin was born
! I'd highly recommend installing it when you get the chance.
is testing canonical URLs right now as well for its clients. It's a great feature for any content management system that has multiple paths to the identical content. You can watch a movie about canonical URLs here
... or you can just ignore it as some goofy geek thing. Either way - install the plugin. I promise it will help!