Ok, I'm done talking about speed effects. Before I go, here are a couple of external links on the subject.
Secondly, in a previous life I wrote an article for one of the ShaderX books describing the detail texture motion blur technique I developed for MotoGP 2. This is not new, but seems worth mentioning here in the interest of completeness. At the bottom of the page is a sample program (with C++ source code) showing the effect in action. No cats though, for which I must apologize. This dates from before I realized that all truly great samples should include cats.
Historical aside: the detail blur sample is actually just a reskinned version of an editor framework I wrote for Climax. If you look in the shaders subfolder of the install directory you will see files such as lerp_blur.shader and specular.shader, which use the HLSL fragment combining system I wrote about here.