Bruce MacEwen references a 2003 article from McKinsey Quarterly by Michael Idinopulos and Lee Kempler, "Do You Know Who Your Experts Are?" in Where Is Sally?, or Knowing Who You Need to Know:
Perhaps the most valuable achievement of a highly-functioning Knowledge Management system is the ability to identify a colleague within your firm who has pretty much the exact expertise you're looking for, when you need it. I call this the "Ask Sally" moment, as in "Ask Sally; she'll know."
Companies tend to know more about their experts than they think they do. The problem is that what they know is spread around databases and reports and the internal context of what all these things mean. While trawling through these things is humanly painful, they are structured for a reason. Set something loose on all the data to find the hidden connections and contexts. The article doesn't suggest this should be used to populate an expertise directory as it could be used as a first pass people search.
The article spends a little time talking about context in the sense that most technical systems are not designed to understand context. They don't have a specific solution, beyond enabling the narrowing of search with context-like keywords (i.e. level of education or seniority, geographic data).
The other important aspect of expertise is that it flows and changes over time. And the best ways to "see" that are to follow experiences if at all possible. Have they written white papers or patents recently? Have they participated in the corporate knowledge networks? What professional meetings are they attending? What did their last trip reports discuss? What is happening on their internal blog?
The interesting thing is the combination of smart data mining with the acknowledgment that the results of an expert search have to be informative enough to help users find who they need to find. Essentially, I hear the need for intelligent hooks into databases / repositories with the ability to slice and dice in multiple directions. Oh, and it needs to be easy to use. This sounds a lot like the new business intelligence tools that provide access to data as well as the capability to interact with it intelligently.