The stove we bought when we built this house had a lovely set of porcelain-coated grates for the stove top.........unfortunately, they were grey, so every bit of cooking detritus stuck to them, and unless immediately cleaned, burned on.  We found that spraying them with oven cleaner, and placing them out in the sun in a black plastic bag for hours was the most efficacious way of cleaning them.

And, like Joanie mentioned, that was also the way to go with cleaning engines and other things automotive, it's not very pleasant trying to replace a freeze-plug on the block of an engine covered in 15 years worth of oil and grime.