Found two great resources for better understanding the impact of changing the margins.
I was turned onto the first by NPR producer Nate DiMeo, who produced the radio piece about the Margins campaign. In October 2001, a research team of the Penn State Green Destiny Council released a report on the ecological analysis of Mueller Laboratory, a biology building on the Penn State University Park campus. "Mueller Policy Paper #1: Reduce Standard Margin Settings", derived from the report, showed how PSU could save 72 acres of forest and over $120,000/year by reducing the default margin settings campus wide.
I was verrry happy to see this proof that small changes = big savings. Because let's get real...while I'm sure there are indeed a few individuals at large institutions and corporations who truly care about ecological issues, there are a heck of a lot MORE people who care about about cold hard cash. Plus, since the report was issued in 2001, I'm only imagining that the savings have gone up as costs have risen.
For those who like their stats a bit less technical, check out Janelle Palmer's Michigan State University Copy Paper Study. She did the report for her semester study, and it's a nice easy read about steps to take, including margin changing. Palmer references the Mueller Policy Paper in her document.