Overview of Ratings Systems
I've found some prior art related to rating things, with respect to syndication. RVW defines an item, a rating (expressed as a percentage), link where more info can be found about the review subject, and a buylink; seems to be designed for product reviews. Uses Dublin Core to define the "thing" being talked about (i.e. a CD, a book, a blog post) using dc:subject and dc:identifier. The spec seems to be pretty loose and also has the disadvantage that it doesn't give a way to distinguish between the rating that I've given a post and the rating that everybody else has given a post. TypePad TypeLists defines a way to publish book and music ratings, uses RVW and Atom. LaughingMeme and Ken Mc Cloud
AmphetaRate defines a ratings API for their ratings and recommendations service. It's not especially RESTful (GET used to submit ratings). Rating scale is 1-10, but the recomendation is to use 0,3, 5, 7 and 10. Documented output for creating ratings is structured text, RSS is the documented output format for getting recommendations. This interface will report either the highest rated feeds or the feed recommendations, depending on the global parameter.