All OER have a life cycle: creation, publishing, repeated revision and reuse, senescence, death. Much effort and many resources have been expended on the creation and publishing of OER. The actual value of such resources, however, depends largely on the extent to which repeated revision and reuse can be sustained before the inevitable onset of senescence and death. The issue of sustainability is largely one of resources, and is a topic of considerable interest in the field of open education.
Via Andreas Link