Tim Berners-Lee wrote:
And on Amazon people say "I found this review useful" to
like the review on the product being reviewed, separately from
rating the product.
So there is a lot of use out there which involves people expressing
stuff in general about the message not its subject.
yes, common use case, many sites give karma to comments / reviews and
have links to them both in and out of context.
When the cost os just fixing Microdata syntax to make it easy to
say things about the subject of a page.
far from expert on microdata, but @itemid may well cater for this.
