@Tedster - sounds like this was second guessing how to weight various factors. 12,000 is a good size but why not implement full natural selection? If the goal is to present the best results as judged by users, that's the way to go (actually put the tweaking power in users hands).
As an aside, an interesting alternative would be to offer the user a set of sliders on the search page. Such as concise content - detailed content; popular - academic; textual - multimedia rich;