This is not particular to Corgis, but it does mention that dogs such as herding dogs, bred to work closely with humans, tend to be smarter. I'll only copy the beginning of the article here, and the link leads to the rest:
"Your dog may not actually be smarter than somebody's honor student -- popular bumper stickers aside. But your canine companion might well be smarter than their toddler, according to a growing body of research on how dogs think.
Using adapted tests designed for human children, psychologists have learned that average dogs can count, reason and recognize words and gestures on par with a human 2 -year-old.
"They may not be Einsteins, but are sure closer to humans than we thought," said Stanley Coren, a professor emeritus at the University of British Columbia and leading researcher on dog behavior.
Coren planned to present his research Saturday at the American Psychological Association's annual convention in Toronto, Canada.
He said the average dog can understand about 165 words, including signs, signals and gestures. They can also count to about 5, he said."
http://www.cnn.com/2009/LIVING/personal/08/07/smart.dogs/index.html