This sounds great, right? But consider the recommendation engines that are part of Amazon, Stack Overflow, whatever. You've just filtered out pages that have a

This sounds great, right? But consider the recommendation engines that are part of Amazon, Stack Overflow, whatever. You've just filtered out pages that have a shirt without stripes on it ... but have a striped shirt somewhere in a recommendation bar on the page. I've run into so many variations of this. You can search for something only to have the recommendation/related results embedded on whatever page to throw off your results one way or another. I genuinely think that whatever standard HTML/XTHML is at ought to have, either as an attribute or a semantic tag, some kind of "related" or "recommended" ability to set that content apart. My cynical thought is that even if it were adopted, it would probably get abused in some fashion.