11. A non-transitory computer readable medium storing instructions configured to cause one or more computers to perform operations comprising: receiving first content authored by a first author; determining that the first author has no assigned rating; and in response to determining that the first author has no assigned rating: identifying attributes of the first author; identifying other authors that are not authors of the first content, each other author having one or more attributes in common one or more identified attributes of the first author and not an author of the first content, and wherein at least one of the other authors has at least one attribute not in common with the first author; for each identified attribute of the first author in common with an attribute of one or more other authors, generating a rating for the identified attribute based on ratings that are assigned to the other authors having the attribute, the ratings that are assigned to other authors being based on user feedback; generating an initial content rating for the first content based on the ratings for the identified attributes; and assigning the initial content rating to the first content.
11. A non-transitory computer readable medium storing instructions configured to cause one or more computers to perform operations comprising: receiving first content authored by a first author; determining that the first author has no assigned rating; and in response to determining that the first author has no assigned rating: identifying attributes of the first author; identifying other authors that are not authors of the first content, each other author having one or more attributes in common one or more identified attributes of the first author and not an author of the first content, and wherein at least one of the other authors has at least one attribute not in common with the first author; for each identified attribute of the first author in common with an attribute of one or more other authors, generating a rating for the identified attribute based on ratings that are assigned to the other authors having the attribute, the ratings that are assigned to other authors being based on user feedback; generating an initial content rating for the first content based on the ratings for the identified attributes; and assigning the initial content rating to the first content. 15. The non-transitory computer readable medium of claim 11 , wherein one of the attributes is a membership of the first author and the second author in a same group, the group being defined by a membership list of authors that are members of the group.