Thanks for the kind words.
The inactivity controller demo is used to show off how you can use the inactivity controller build into Farseer Physics Engine to make the bodies sleep after some time. It takes some tweaking to get it right, but it can drasticly increase the performance
in platform-based games where most of the geometries are active when the player is near.
The inactivity controller itself can actually have a big performance impact - It iterates all the moving bodies in the world to see if they should sleep. So use it wisely. For Farseer Physics Engine 3.0 we are working on a better implementation of sleeping
bodies that only wake up when needed. This increase both stacking stability and performance - but it also has its limitations.