I suppose the question to be answered is what makes a social document different from a weblog, I think it is the sense that the publication is a one off activity or from a fixed corpus of content eg a book, consultation doc etc. Rather than a weblog where the content is continually added to or a message board where the audience continue to add content at liberty.
There is a reader vs publisher vs content owner three way split, it is not about the software used, it is the ownership of the content that makes the key difference. My personal weblog takeoneonion is a blog, so is plasticbag. TheyWorkForYou is a social document, as is talkeuro and pepys diary
The key difference is that the people creating the site didn’t create the content on the site, parliament did or sam pepys did. This also works as a definition for del.icio.us and connotea too.
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more examples of annotatable documents More examples - annotated cpan