Thanks for the detailed reply. I couldn't really find any details on the actual RSM sampling except some shader code in the Crysis paper to downsample it. I'll try implementing what you mentioned. Is this similar to creating stable shadow maps?
Also does this also apply to using a perspective camera or only an orthographic projection? In case I wanted to do a spot light do I need to do anything special?
Unfortunately I'm stuck with opengl or dx9 right now. Unity3D version 3 also doesn't have tex3d.