This sounds pretty cool. More opportunities for creative mashups using familiar characters:
GAMEFEST: Landmark legal move allows consumers free use of Halo, Forza and Viva Piñata assets in homebrew works
After announcing the 2.0 version of XNA Game Studio during Gamefest's keynote, XNA general manager Chris Satchell also revealed that the company had made an "unprecedented" move to allow consumers direct, legal access to game content from a number of Microsoft-owned IPs.
Effectively immediately, Microsoft has granted consumers "a personal, non-exclusive, non-transferable licence to use and display Game Content and to create derivative works based upon Game Content, strictly for noncommercial and personal use".
The licence, similar to the Creative Commons agreement that some writers and artists use to give their works free and open copyright to the public, gives users access to any game published by Microsoft Game Studios (but not any third-party brands). Users don't get rights to share the games themselves, but can share creations that use game content.