Thanks to Mike Smith who pointed me to this summary of a talk given by Eve Gray at the Creative Commons South Africa launch. Eve is from the Human Sciences Research Council of South Africa, and:
discussed how HSRC’s early experiments with open access publishing paid off. As they made their research papers available for free download, the print revenues went up by 270%.
This is exactly the same experience I had with my first learning objects book back in the day. Nice to see more data coming in to support this argument.