The computer industry group says that "fair use" attributes $4.5 trillion to the US economy.
Here's the article (http://informationweek.com/news/showArticle.jhtml?articleID=201805939).
If you like reading tables and graphs, you can read the report here (http://www.ccianet.org/artmanager/uploads/1/FairUseStudy-Sep12.pdf).