Here is a recent article from the Boston Globe about Human Capital Contracts. As you will see in the article, the drawbacks to human capital contracts are either easily overcome, or are outweighed by the positives.
An excellent book about the subject about investing in the potential of people. This book provides a wide variety of types of human capital contract and related mechanisms.
This book explores the possibilities and outcomes of human capital contracts from a statistical perspective. A fine resource for those looking for the a good quantitative exploration.
A different view – internal human capital investing from the perspective of the funder, and in particular the corporate investor.