In October (2012) I started a workshop to learn the basics of Houdini.
In the forth week, we simulated debris flying off an object such as for example after a bullet hit. We learned to create our own collision system with VOP POP by using volumes. That way, when the particles enter the volume, created from the selected mesh (in this case the boxes), they get pushed back out.
I tried to stress the system a bit by using a bit more complex mesh, but it seemed to handle it pretty well.
For the effect, I create a circle of which I edit the normal information, scatter points onto the surface and then I copy those onto the points of a curve. Before the copying, The points get deleted with "$PT == $F / 3" and then rayed, with a Ray SOP, downwards onto the boxes. Then with a PopNet, poof go the particles along the normals of the circles. The particles get directed a bit with a force, drag, curlnoise and the collision VOP POP.