Legal Question in Intellectual Property in California

You need to check the Terms of Use/Service. I have not done so, but understand that selling in-world gold in exchange for real world money violates the Terms in World of Warcraft. You should check the terms before attempting to sell.

Violation of a game company's terms of use could simply be a breach of contract, not an intellectual-property misappropriation. In doing a little research on this subject, I did not find any reliable decided appellate cases, and although there is legal skirmishing going on both here and abroad, I think we are going to have to wait and see whether "gold mining" violates any intellectual-property laws such as copyright law, and/or whether legislatures here and abroad will take any interest in writing new laws.