Measurement, engagement, and libraries

Just read a post by Andy Lark at BrandShift ... he mentioned that the advertising industry is in the process of reimagining (apologies to Tom Peters) the way they will measure (and eventually charge for their work ... this new measurement is engagement ... Mr. Lark says:

"This will only become more important as communicators discover the need to measure the degree to which customers are participating in their communities and brands. The best campiagns will measure what changed: did we move markets, change minds and increase sales? This isn't just about driving communications accountability, its also about driving marketing accountability."

So my question is ... how do we measure our ability to produce real change for real people? How will we measure how we helped change minds and improved our communities? The answers will define our legacies ... and it will drive library accountability and be the next step to governmental accountability.