For those that are interested in creating callouses, the chinese do have some sort of concoction that speeds up the process somehow.
Knuckle push-ups on concrete or gravel will do the trick real quick. Ensure that only your punching knuckles are in contact with the ground and if you are really tough, twist your knuckles as you push yourself up. I used that technique to just get in the habit of using the two knuckles for a punch, but after they were beaten to a bloody pulp they formed callouses... in just about three weeks time.
It'll actually take a long time using the makiwara to get callouses because not 'real' damage is being done to the knuckles (unless you are leaving blood stains after the drill). In order to get the body to react, you've got to give it something to react to.
And, I'm with Cthulhu, I don't actually advice doing that because it is pretty much useless in this day and age. Toughening the hands was for punching through bamboo armor that the samurai wore. Once people start walking around wearing wood breastplates, then I'll start trying to develop callouses on my hands. Until then I'm going to give my girlfriend something the will actually want to hold onto and be confident in the knowledge that it only takes a mere 10-20 pounds of pressure to do serious damage to the human body and can generate several hundred (thousands with some techniques) pounds of pressure with my hands as they are. :EG: But you'll do as you will and I wish you the best of luck...