redefine the relevance of search results
I'm not sure I really see the use case here. Surely what one wants when one searches is that for which one searched... for example, when I search for 'the register' (on DDG) the register front page is the first hit, and almost everything else on the first results page points at vulture central. I don't see how one would change the relevance of that.
I can certainly see the utility of getting rid of clone answer pages - they're only there to benefit from the users of an authoritative site and they sooner they disappear, the better.
But I can't help feeling that a more focused search engine - particularly one in which I can exclude things easily - would be more helpful. I don't think I really want a thousand pages of advertising links (which I'm going to block anyway) while I'm trying to find substitutes for electronic parts, or how loud a sparrow is in dBA (the internet is really failing me on this last one!).