http://ati.amd.com/developer/ShaderX2_MotionBlurUsingGeometryAndShadingDistortion.pdf^^ if someone is feeling a bit clever

it actually has a lot of the shader there. i didn't look at it enough to determine how much is directly usable with GS, but it looks good! i think their implementation would work better with balls than complex objects, but i've got some ideas that could be used with animated objects if i have time this weekend.
julz