Just back from a rain sodden trip along a track south of Auckland. Came across a stuck Toyota Surf. The driver had done this and that, tried it in low range, tried it in high range, and it just sat there spinning its wheels in the slush. I studied the situation for a minute, went to the front wheels and locked the manual hubs. "Try it now." The Surf drove out like it was on tarmac. How common a mistake is that? How big a prat do you feel when you've made it? How superior do you feel when you've fixed it for someone else? I can now answer both the second and third!
About the hubs: Wikipedia has a good article on the subject here.