What few people know is that the first Double Clutch Gearboxes were invented for racecars in the 70ies. Porsche built one to save tenths of a second per lap in Le Mans and on other race tracks. As we know changing a gear (manually) takes time. So being able to shift instantly from one gear to the other seems to be a good idea. However the Porsche box wasn't a success and Porsche dropped the idea. Many years later Volkswagen started to equip cars with DSGs that offered the convenience of automatic gearboxes while not taking the extra fuel traditional automatic gearboxes sip. Audi followed soon and today many car manufacturers add DSGs to their street cars, including Ferrari (California Spider), Porsche (911/911 S), BMW Z4 35si, etc. However in racing we haven't seen one of these gearboxes. Why? Well they get much heavier than automated sequential gearboxes and they can't shift much quicker than what you can buy for example in a 430 Stradale or what Formula 1 has demonstrated. Weight is bad in racing, too many moving parts are bad for reliability, cooling needs when high power is involved and other issues add to the disadvantages.
So, what is good for street cars doesn't make sense for race cars. It shows that people appreciate the higher gear change comfort of DSGs while they hate the bumpy gear changes of automated sequential boxes. Well, almost. For fast road cars manufacturers actually program bumpy gear changes or noise effects to create the sensation of a sporty gear change.