The Association for Library Collections and Technical Services Preservation and Reformatting Section has released a draft of its Minimum Digitization Capture Recommendations. The comment period ends on 12/31/2012.
Here's an excerpt:
This document was created as a guideline for libraries digitizing content with the objective of producing a product that will not be re-digitized at a later point. Institutions can feel secure that if an item has been digitized at, or above, these specifications, they can depend on it to continue to be viable in the future. These guidelines only speak to the technical specifications of the digitized content itself and not to the larger issue of digitally preserving said content. In some cases, institutions may want to request a digital copy to preserve themselves further safeguarding materials by preserving them in multiple locations.