I am in the Educational Advances in Artificial Intelligence (EAAI-13), and we just concluded a session on educational repositories, particularly online repositories of homework assignments. Repositories of educational resources is a topic near and dear to my heart, but at least in the case of repositories of homework assignments, there appears to be no, little, or at best weak anecdotal evidence that assignments are being reused. At a minimum, don't we want repositories to be "instrumented,", like my (and everyone's) YouTube channel(s), so I can see downloads, likes, dislikes, and more sophisticated measures of usage that are specific to homework assignments?
Its hard to know if a homework assignment that has been posted in a educational repository is actually used by another instructor, unless an instructor who has used it, gets back to me and tells me so. There is some work in thinking about how to do this. But there is also low hanging fruit. First, we can measure downloads, but beyond this, as an educational community can take a small step towards a scholarly culture surrounding education materials by designing licenses specific to this kind of content.
For example, a license for usage of educational content could require that the material can be used by others (e.g., following any of the principles of creative commons licenses: http://creativecommons.org/), but additionally require that the user report back on the usage to the author (typically, the copyright holder), whether the use is as is, or derivative.
I think that this would be an incredible help to evaluating the extent and manner of use of educational material, going well beyond measuring downloads, and ultimately of evaluating the utility of educational materials to the educational community.
Let's ask people about their use, through a license that requires report back (and nothing else), rather than simply depending of the ability of inference by machine methods.