If you are at WordCamp 2007, one of the best sessions was Google’s own Matt Cutts discussion on optimizing your WordPress blog. You can see the whole presentation over on John Pozadzides site’s One Man’s Blog. Here is the link. You can see in Matt’s Whitehat SEO tips for bloggers slide show that one of the things that WordPress “suffers from” is that you can reach the same data from multiple sources.
You can get to the same article by browsing by category, by day, month, year etc. etc. etc. Each time Google sees the same data repeated on your site again, it hurts your site a little bit more.
This bit of code will help fix it. It goes into the header part of your blog and will tell Google that it should ignore all of the pages that are not the orginal source of the article.
Here you go:
if (is_home() || is_single())