Autodesk was defeated in the first round of this battle in Seattle US District Court, May 21 2008:

Read Vernor versus Autodesk

Judgement Announcement

Interestingly, Autodesk is also resorting to more and more desperate measures to attack the Open Design Alliance:

The issues around this ruling are complex and a final district ruling is not due until June. But it could serve as an important benchmark for similarly licensed software sold by other companies. Such decisions can ultimately challenge the legal position that software EULA take, restricting the customer’s use of software they have paid for.

That being said, many modern software programs like AutoCAD still require an activation from the vendor for each new installation. I offer one guess as to whether Autodesk would nicely re-activate a used serial of AutoCAD 2006 that someone buys "arguably legally", but second-hand.