How to measure "success" in training?

With the emphasis on 'competency-based' training, how do you measure success? Particularly with the complex responsibilities of graduates of public health management or field epidemiology training programs, what do you measure that can inform your program's direction? Process indicators abound: number of graduates, costs per student, stacks of materials that have been produced. But does it have an impact? This is a challenge for almost any job, in hundreds of industries throughout the world. Particularly with managment or leadership development, many are only able to articulate "I know a good manager when I see one".  Employee surveys are a good data source, as are exit interviews when employees leave an organization. What are some ways you have used to measure 'good' managers?