Very interesting 'Legally Speaking' article in the March 2009 CACM, When is a "license" really a sale? by Pamela Samuelson. She covers the principle of 'first sale' and the recent decisions on the UMG v. Augusto and Vernor v. Autodesk. Essentially both Augusto and Vernor were selling used CDs and Software on eBay and the copyright owners of the products went after them for these sales. Both parties are using the first-sale doctrine to defend their rights to sell the media. The copyright owners are trying to use contract law and the licenses to restrict transfer of the physical media and right to use it. Samuelson predicts that both will end up on the 9th Circuit appeals court.
I hesitate to issue an opinion here, I see both sides. More debate here, here and here. A nice little post on first sale here. From the perspective of books and music, I side with the first sale doctrine.. and mostly think the 'one click' license notices as having many problematic issues. If you receive a physical copy of something for $$ or as a gift, you should be allowed to resell it at your whim.
It's worth hunting down the previous articles in this series.. they stretch back many years.