Ballerinas first used darning to strengthen the toes of their flat shoes and so to allow them to go on pointe. Modern shoes, obviously are made with tons of glue etc in the toe box to make them strong for pointe work, so darning isn't totally necessary. I never did it myself, my shoes were pretty long lasting for me. But I knew girls who took their shoes to a cobbler to have a rubber like material attached to the toe, or to have a leather like material attached (sorry I don't know the exact materials used). Obviously darning is probably cheaper than this, so check out this tutorial from Freed: http://www.freedusa.com/magazine/14_6_tips.html
In addition, I've read that you don't have to go through all the layers of the toe box with your needle, just enough for a secure stitch (http://www.ballet.co.uk/dcforum/training/634.html#9. You can also customize what you do, so if you tend to roll out to either side of the box, you'd sew extra layers on one side.
Hope this helps!