At the lower end of the scale, I ordered it for breakfast at a diner here a few years back, and was disappointed to find it was JUST the canned variety in spite of being described as a "specialty" or some such. And of course it wasn't lovingly crisped in a skillet like we do at home. It might as well have just been popped into the microwave for a quick heating.
I love the canned stuff, like I said, but it's a whole different thing from a real homemade corned beef hash with, you know, real corned beef. Restaurants should state it like it is, either way, and I'll be happy.