Lessig writes on this major ruling.
In non-technical terms, the Court has held that free licenses such as the CC licenses set conditions (rather than covenants) on the use of copyrighted work. When you violate the condition, the license disappears, meaning you’re simply a copyright infringer. This is the theory of the GPL and all CC licenses. Put precisely, whether or not they are also contracts, they are copyright licenses which expire if you fail to abide by the terms of the license.
Full post from Lessig.org here