Let us talk about the marginal product of worker i in occupation j. In most cases, this is indeed zero. My marginal product would be zero in fishing, medicine, and many other fields. In a complex economy, if you were to randomly assign workers to jobs, ZMP (zero marginal product) would be the norm, not the exception. The more complex the economy, the more carefully workers must be assigned in order to avoid ZMP.
-- Arnold Kling

Cue educators' and students' worries about portable skills and finding jobs that can found careers. Job selection's just going to get harder, so we'll hopefully see some innovation along these lines: perhaps a mapping of tested aptitudes to forecast skills demand? Essentially a mashup of US Occupational Outlook and aptitude/psych tests.

This assumes that jobs are difficult and complicated to learn. This may be true of some jobs that are extremely memory intensive like being a lawyer, doctor or mechanic. There are plenty of jobs that seem much more driven by aptitude, though, like programming or driving where experience is functionally (this isn't to say that it isn't desired in real life, just that it doesn't seem to make much difference in employee job performance) less important. Also, here is the interviewing meta-study I told you about earlier. http://bobsutton.typepad.com/my_weblog/2009/10/selecting-talent-the-upshot-from-85-years-of-research.html
Weird that work sample tests seem to work better than an actual trial period. What does he mean by structured interviews? --Rehana
Basically ask the same job-related skill-test questions of all candidates. See my entry for TheHandbookOfInterviewing