Google Now Supporting rel="canonical" Across Domains By Chris Crum Google announced that it now offering cross-domain support of the rel="canonical" link element. If you are unfamiliar with this link element, Google's Matt Cutts discussed it with us here. Basically, it's a way to avoid duplicate content issues, but until now, you couldn't use it across domains. "For some sites, there are legitimate reasons to [have] duplicate content across different websites — for instance, to migrate to a new domain name using a web server that cannot create server-side redirects," says John Mueller, Webmaster Trends Analyst with Google Zürich. http://www.webpronews.com/topnews/2009/12/16/duplicate-content-owners-catch-a-new-break-from-google
How much resource Google have to use to figure if a content is canonical. However its a good thing to intriduce.
It would be nice if they at least gave a real life example of "how" the code is to be used instead of just talking about it. After reading the article, I under "why" and "where" to use rel="canonical", just not "how" to use it.
You would think that Google would be smart enough to figure this out with creating additional burden for the Webmasters. Google just wants to control every aspect of web marketing and try and force people to use their services.