As the above chart shows, sweet potatoes at one time had a small niche in the American dining repertoire. But after WWII for, some reason they fell out of favor. It could be because we started eating so much cheese:
But there are indications that the sweet potato is making a comeback, especially in Europe:
With U.S. consumption growing slowly, farmers have found a market for the vitamin-packed, cholesterol-free sweet potato on the tables of health-conscious Europeans. Between 2005 and 2009, the value of U.S. sweet potato exports more than doubled to $51.4 million, with much of that growth coming from Europe, especially Great Britain.
I tried to grow sweet potatoes in the garden a couple of years ago without much success. I'll have to give it another go next summer. In case you're wanting to grow your own, you have to order them as small dry root plants that you then plant in the ground. It's different from other varieties of potatoes. Irish Eyes is a good place to order the starts online.