There's nothing that I can add to this ars technica posting:
Read the entire post. The key to the ruling is that the judge decided that the Autodesk software was sold, not licensed, and therefore the First Sale Doctrine applied.
A federal district judge in Washington State handed down an important decision this week on shrink-wrap license agreements and the First Sale Doctrine. The case concerned an eBay merchant named Timothy Vernor who has repeatedly locked horns with Autodesk over the sale of used copies of its software. Autodesk argued that it only licenses copies of its software, rather than selling them, and that therefore any resale of the software constitutes copyright infringement.
But Judge Richard A. Jones rejected that argument, holding that Vernor is entitled to sell used copies of Autodesk's software regardless of any licensing agreement that might have bound the software's previous owners. Jones relied on the First Sale Doctrine, which ensures the right to re-sell used copies of copyrighted works. It is the principle that makes libraries and used book stores possible. The First Sale Doctrine was first articulated by the Supreme Court in 1908 and has since been codified into statute.
There's also an excellent post on William Patry's blog, with some very lively and extensive discussion that is itself worth reading.