In the October, 2008 issue of the MLA News, Terrance Burton presented a quick overview of how the business, dollor-based Return on Investment approach (profit gained from invested dollars) can be expanded to a view of what value is derived from whatever inputs you choose to work with.  This can be more relevant in the library world, where profit is not the main point.  In fact, in many health-related institutions served by libraries, profit is not the main point.  Money is indeed invested in libraries, but it can be challenging to assess the outputs from that investment.  Burton suggests that we identify outcomes that we want to measure, use a mix of approaches (quantitative, qualitative, speculative), and accept that any measure will be flawed.  Despite flaws, using mixed approaches can provide various indicators to bolster a case.