TheMadScientist - 4:17 pm on May 4, 2011 (gmt 0)
Just to make sure there's a complete understanding of what the canonical link element will and, more importantly in these cases, will Not do:
Will: Work intra-domain. Or, iow within a domain, including subdomains, a canonical URL will be used as a 'strong indication or hint' as to the 'preferred URL' for the content. EG example.com to www.example.com is fine and will be recognized.
Will Not: Work across domains. Or, iow a canonical link element on example.com will Not be used if it points to some-other-example.com.
It sort of has to be this way for security reasons, imo, because if a person does not have server access to set a 301, in some situations there may be a reason other than the host not supporting it, such as limited access, and if it was supported cross-domain then an unauthorized person could effectively move a site without permission, so it's great 'on-domain', but not effective cross-domain.
This is just a clarification, because I see it's use recommended quite a bit, and I thought this was a good thread to point out the limitation for readers who might not understand: To move to a different domain you really need to use a 301.