Now I think I know the "correct" definition as per the Joy of Cooking: sweet potatos are yellow with brown skin, yams are the very orange ones with red skin.
However I'm really confused about usage. Here in Toronto I don't believe we have any true "sweet potatos" - although there are more tubers at the grocery store in recent years - I believe they're cassava and such, purchased by the Carribean and African communities. But outside of 'ethnic' cooking I don't think Canadians do these at all. We do eat what we call sweet potatos, which apparently are in fact yams.
So where are you from and how do ya'll make sweet potato pie? sweet potato cake? sweet potato fries? I always assumed with YAMS, just like we do, but I'm starting to wonder.