We also looked at findability in a very interesting way. While every 'expert finder' application focused on building a better fishing rod to catch the fish, we focused on nudging more fish to come out and thrive. We focused on encouraging people to share empirical data about themselves on their profile by promoting their brand and showing them the value of sharing. Inspired by modern profiles in the consumer world we surfaced and presented information about a person in a very compelling manner in the person's profile. Our hypothesis is that if enough empirical data is revealed by a person on his or her profile in the context of their day to day work, a regular search engine will be able to find that person and present them in context for the 'expert seeker'.
By the way, I have seen every expert finder application that tried to build just a great search engine fail. No matter how good the search, if people don't share empirical data about themselves no one can find the right expert.
You also need to build tools for the expert and the expertise seeker to engage. You need to build an incentive system for the experts as well. More about that later.