If you fast forward the video to 12:18, the commentator says that they prevent abuse by not allowing this tag to be used across different domains. However there is a pop-up on the video that says the rules for this tag have been changed to allow it to be used across domains.
Here is that link:
http://googlewebmastercentral.blogsp...ss-domain.html
Quote:
Handling legitimate cross-domain content duplication
Tuesday, December 15, 2009 at 2:47 PM
Webmaster level: Intermediate
We've recently discussed several ways of handling duplicate content on a single website; today we'll look at ways of handling similar duplication across different websites, across different domains. For some sites, there are legitimate reasons to duplicate content across different websites — for instance, to migrate to a new domain name using a web server that cannot create server-side redirects. To help with issues that arise on such sites, we're announcing our support of the cross-domain rel="canonical" link element.
Ways of handling cross-domain content duplication:
Choose your preferred domain
When confronted with duplicate content, search engines will generally take one version and filter the others out. This can also happen when multiple domain names are involved, so while search engines are generally pretty good at choosing something reasonable, many webmasters prefer to make that decision themselves.
Reduce in-site duplication
Before starting on cross-site duplicate content questions, make sure to handle duplication within your site first.
Enable crawling and use 301 (permanent) redirects where possible
Where possible, the most important step is often to use appropriate 301 redirects. These redirects send visitors and search engine crawlers to your preferred domain and make it very clear which URL should be indexed. This is generally the preferred method as it gives clear guidance to everyone who accesses the content. Keep in mind that in order for search engine crawlers to discover these redirects, none of the URLs in the redirect chain can be disallowed via a robots.txt file. Don't forget to handle your www / non-www preference with appropriate redirects and in Webmaster Tools.
Use the cross-domain rel="canonical" link element
There are situations where it's not easily possible to set up redirects. This could be the case when you need to move your website from a server that does not feature server-side redirects. In a situation like this, you can use the rel="canonical" link element across domains to specify the exact URL of whichever domain is preferred for indexing. While the rel="canonical" link element is seen as a hint and not an absolute directive, we do try to follow it where possible.
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Even though we're tiny and look at Video Secrets as masters of their domain, I'm pretty sure that this tag isn't used to bump up their ranking and diminish their affiliates ranking. I'm still reading and learning about this tag and still have found nothing to do with ranking. I could be wrong but chances are it's just used to manage duplicate content and nothing else.