well I guess I was the first who try to do curve blur
I was very inspired from those real life photos
my first attempt was using multi-angle blur approach
then I discovered using twirl to un-curve the road for radial zoom blur
however it also required free transform the background to match a perfect circle shape like your method here
but the difference was I using zoom blur and you using spin blur
another important discovery is by Revolution
he found Paint shop pro 9 can do radial twirl blur by one step
I tried PSP9 for a few of my work
but I found PSP9's blur filter very user friendly
you can even set the exact point for radial blur center
but blur quality is not as crisp as photoshop counterpart
Adding noise before blur is my thing too
it adds more detail to the road like those real life photo
but I only put noise on the road where it's close to the camera though
A sample of real life photo
it is obvious that the Porsche artist used twirl blur technique but not perfectly done
the flaw gave me the idea of using twirl
sorry for the lengthy reply and a bit show off