Canonical tag for duplicate content

Google, Yahoo and Microsoft Live recently announced support for a new "canonical" tag that their spiders will recognize. It's purpose is simple: when you have deliberately created duplicate content, this tag tells the search engine where the "canonical" content lives - that is, the page you'd prefer they pay attention to for listing results.

As an example, back in the days when tracking SCO Unix stuff was important to me, I created a "Bofcusm" directed and would put copies of relevant and interesting newsgroups posts there. However, there was one poster, "Bela", who made a lot of useful posts, so I duplicated his posts to /Bela. People who only wanted to read his stuff could find it all there but obviously this is dreaded "duplicate content".

The new tag solves that. In the Bela articles, I can tell the search engines that they should look to /Bofcusm for the "real" content. If the Bela article is 1735.html, the tag looks like this:

 <link rel="canonical" href="http://aplawrence.com/Bofcusm/1735.html" />
 
 

I also did the same thing with the pages generated by the "Printer Friendly" links. That shouldn't be necessary as my robots.txt tells spiders not to go to those pages anyway, but who knows if this will help some other thing at some other time.. I figure it can't hurt.

Now I just need to figure out if there are any other conditions where I've duped content, on purpose or otherwise.