A friend at Penn State’s University Libraries shared this resource with me. It’s a page within the Pennsylvania Center for the Book site which addresses copyright basics, including a definition and some examples of cases where you can duplicate copyrighted material. There is a section of this page that describes “First Sale” – which essentially gives you the right to sell things like used books and CDs. I looked up a bit more about First Sale on Wikipedia and there is a 2008 case listed where the court ruled that selling used software was legal. Very interesting stuff.