Comment
Comments are a feature of most entitities
Comments include a score so that comments can be propagated automatically using some variation of extended w:FOAF for example.
Almost everything can be commented by almost anyone, though there will have to be restrictions of somekind because otherwise there will be lot's of disinformation and potential for lawsuits.
Comments will mostly be on products, companies, product groups and of course other commentators.
Special rights could be reserved for companies to veto comments that are disinformation