At every level of racing, parts are modified by hand in an attempt to gain a bit (or a lot) of performance through well-educated guesswork. What, then, once a week's worth of effort with a die grinder yields something that works? Geomagic has a neat little case study that involves an intake manifold for Kevin Harvick's Nextel Cup car. The geometry of this custom part was worth 5 HP (a huge improvement at that level of racing), but reproducing such a part by hand can be dang near impossible.
The company provided software that allowed Richard Childress Racing to scan the part with a CMM, pull it into ProE, and then reproduce as many parts as they wanted on a CNC machine in one-seventh the time it took to duplicate the part by hand, and likely with far better tolerances. For us mortals, companies like CNC Cylinder Head can perform similar services, and with the decreasing cost of such equipment, it wouldn't be surprising to find such a setup at your local machine shop in the not-to-distant future.