Determining sentiment (the topic of the NYT piece) is considerably harder though, because it would allow for spammers to write negative articles about a site an

Determining sentiment (the topic of the NYT piece) is considerably harder though, because it would allow for spammers to write negative articles about a site and link to it and negatively affect its rankings. This could be solved by making sentiments act as a weight (i.e. a multiplier in [0, 1]). Positive sentiments would give a particular reference more weight, negative sentiments would give little to no weight. Then it would be impossible to negatively affect a site's rankings - only positively affect them. Just like now.