Gamasutra - Features - Minecraft, Intellectual Property, and the Future of Copyright
This article discusses IP protection and whether a game developer like Mojang can be held culpable for what its players construct in-game if the constructions resemble IP of another company, e.g. logos, buildings, characters.
Interestingly, Notch said on reddit:
Originally Posted by http://www.reddit.com/r/technology/comments/okp8i/mojang_joins_sopa_protest/c3i47tv
One of the biggest reasons why Minecraft got as big as it did is because people talked about it to their friends. They posted screenshots of the game, recorded videos of it and put it online. Without sites like twitter or youtube, Minecraft wouldn't have gotten as big as it did. And besides, we DO host user created content in the form of skins, some of which infringe on existing copyrights.