I have found that chalk actually helps. I believe that the reason for this is because the bar is less likely to slid in your hands when they are chalked up. I also think that the chalk toughens them up a bit.
I do agree that they require a little maintenance. Sometime I use my girlfriends stone thing. I forget what it is called, but it is probably the same thing the as the foot sander thing.
Actually, the only reason I started doing this was to stop scratching her with my pointy callouses. It is a coincidence that it also had another benefit. More often then not, I use piece of fine grain sandpaper. As long as you don't let them get too big and chunky you should be good to go.
Callous maturity also help. Before my entire hand was a callous, I used to tear the ones at the base of my hand often.
I also agree with Phill on the grip thing. As my grip has got stronger I tend to tear them much less.