Relevancy engines might specialize by profession. Doctors, for instance, have many records documenting specific licensures, skills, and their experience. I'd want a relevancy engine to balance, for instance, the number of times she performed a particular procedure against success rates, certifications, and special training. In comparison to other candidates. Compared to their fellow alumni.
Candidates are more than their resumes or profiles.
Some relevancy services will exploit this by scoring soft qualities. Many tools exist for assessing work styles, communication styles, value systems, career goals. New tools for team assembly will also enter this category. This is useful to the degree you look for work or workers who are friends of friends, creating other referrals. SixDegrees works like this a little but is not integrated with other services for this purpose.