Canonical tags for syndicated content?

[Peter K. Lam]

I know a lot of companies syndicate their content either via RSS or the allow other sites to use their data through providing an feed. Traditionally rel=canonical is used within your own site to let spiders know which page on the site is the originator and the rest are duplicate. Has this methodology ever been applied to external websites?

In theory I'm guessing that the site that is borrowing content has to have the <link rel="canonical" href="[main page]"> in their page in order for this to work. Has anyone done this before and do you know what kind of value, if any, spiders are applying to these?

Here's some info from SEOmoz about the canonical tag in general:
Canonical URL Tag - The Most Important Advancement in SEO Practices Since Sitemaps | SEOmoz

Thanks for any feedback!

[Peter K. Lam]

*bump*
Does anyone have any insight on this? I haven't found any further information. Thanks.