When people first hear this tip, they're skeptical. But, Microplanes are excellent for getting rid of even the driest and hardest skin on your heels. These have become so popular that Microplane has even developed a special product JUST for removing hardened skin on the bottom of your feet: Microplane Foot File
Use after taking a warm bath, to soften the skin and make it easier to remove the hard calluses. Be careful as these are sharp, and you'll only want to remove a bit of skin at a time, rather than take too much off your heels and cause pain.
After removing hard skin from heels, be sure to moisturize with a rich foot cream. Peppermint foot creams are especially soothing and have a nice cooling feel.