I think the key is that the search is primarily on the symptoms. It is meant to solve problems not be something that is browsed. Keywords/tags/categories of some sort are also needed. Maybe at some point, have a "20 questions" style interface where successive questions are asked until the problem is narrowed down. A virtual bug doctor, if you will.

I'm wondering if using a modified version of Mantis or Trac would work to start off with. Otherwise, Joachim, are you volunteering do to a rails version :) ?