Educause have a useful page on open education and open educational resources at http://www.educause.edu/Resources/Browse/Open%20Educational%20Resources%20OER/27863
In particular, their one page document Seven Things You Should Know About Open Educational Resources at http://www.educause.edu/Resources/7ThingsYouShouldKnowAboutOpenE/205913 contains a helpful rational for the use of oer as well as countering some common reasons given for resistance to oer practice.