This French article has word that a French court has ruled that users should be permitted to resell games and other media purchased through Steam (thanks Primalchrome). IGN has a reaction from Valve saying they will appeal the ruling. There is an article about the ruling on MSPoweruser that outlines it in English so we don't have to resort to Google Translate. Here's word:

“In a judgement rendered on September 17th by the Paris District Court… The Association for the Defence of Consumer Rights managed to obtain the cancellation of a number of clauses that Valve imposed on Steam,” the website says.

The biggest cancellation is that of Valve’s licensing of Steam games. Although you pay full price for titles on Steam, you do not own games you buy on Steam. This ruling changes that: by allowing you to sell your Steam games that you’ve purchased, gamers now have some form of control over their titles. The ruling doesn’t just apply to games. Games, movies, trading cards and more are all included.