In the early days of the neterwebz most of your search results were pretty relevant if you used the correct terms. The world moves really quickly though - and I have been encountering a particular problem where my returned results are relevant...if I'm asking the question 8 years ago. Technology is the worst, but I've even come across medical information that is "woefully" out of date only 3 years later, but because they're being hosted on a more popular site they "become" the popular source, even if they're wrong. Not sure how you could accomplish that part...the next suggestion should be easier.
How about being able to blacklist some sites from your search results? There are forum farms out there that are useless for answering questions, yet because of the way they game the system they are returned high on most searches - find a way to kill those fuckers and you're off to a decent start.
I don't care if you have to set a cookie as long as I can see it and know what it contains. You don't need to know anything about me to know that I don't like bullshit websites