Corset piercing are pretty pointless, they're just supposed to be temporary, just saying. But they shouldn't hurt too bad. Just like any other surface piercing, just a pinch, maybe a little more than facial piercings.
well, if you are ticklish it will hurt like hell O_O
really it depends on the person, i, fo example, dont feel much pain in the area while my Girlfriend jumps at the touch of a toothpick :D
Probably about the same as a navel piercing. By the way, corset piercings are not permanent. You're only suppose to keep them for a few hours.