Derek Slater at A Copyfighter's Musings is all over the eBay digital download experiment, exploring whether the first sale doctrine can apply to digital copies of works. When you sell a used cd, there is at least some chance that you haven't ripped it to your computer's hard drive before doing so. With digital files, you can't transfer the file without copying it in the process.
This dilemma highlights a recurring issue in the application of copyright legislation to new technology. The Copyright Act places a huge emphasis on the act of making copies. You can sometimes use works in ways the copyright owner might like to control, but avoid infringement on what's really a legal technicality, because no copy is made, yet in other circumstances, the incidental creation of a copy as one step in the process of using the work, otherwise allowed under copyright law, is the basis for concluding that there is infringement.
The Center for Internet and Society at Stanford Law School is a leader in the study of the law and policy around the Internet and other emerging technologies.