A web page that definitively satisfies a searcher’s intent is “Perfect,” and should appear at the top of Bing’s search results. On the other end of the scale, spammy web pages and pages that almost no searcher would find useful are deemed “Bad.”
That’s a bit of how Bing instructs the people in its Human Relevance System (HRS) project to grade web pages. It’s explained in a 52-page document that Bing calls the “HRS Judging Guidelines.”
Actually, Adcenter has a similar system to HRS, which is very nicely described in this presentation by Ty Liu (note: slow link to China):
In fact, the Ad Center equivalent of the HRS system, as it applies to Ad Landing pages, is described in this conference proceeding hosted by him, and with a paper :
Look for the paper by Yih and Jiang, entitled ‘Similarity Models for Ad Relevance Measures’.