The United States Court of Appeals for the Federal Circuit has upheld the validity of an open source license, the Artistic License, in Jacobsen v. Katzer and Kamind Associates.
Read more about it at "Court of Appeals for Federal Circuit Overturns Jacobsen v. Katzer—Ruling as Text," "Federal Circuit Says Open Source License Conditions Are Enforceable as Copyright Condition," "Huge and Important News: Free Licenses Upheld," and "The Model Train Patent Story—Jacobsen v. Katzer et al."
Here’s a link to a two-minute video by a lawyer who agrees with the court of appeals decision:
http://jurisvodcast.com/2008/08/17/open-source-copyright-infringement/