Former Coding4Fun guru and now XNA wonk Brian Keller announced on his blog that Microsoft Game Studios has released the source code (note 1GB size) for Mech Commander 2, the real-time strategy game.  

The XNA team released Mech Commander 2's source code to showcase how XNA Build, their new build system can dramatically improve build creation of large size commercial games. The performance benefits show incremental builds were 6x-14x faster using XNA Build.