I learned to use front brakes during mountain biking the hard way.

Me and a bunch of friends were flying down this fast decline that had a sudden and sharp turn. I watched people just barley make it around the corner. My turn came up and all steam ahead seemed to be the order of the day. When I hit the turn I panicked and locked up my rear wheel. Time slowed down and reruns of GI Joe flashed before my eyes. Did I mention that if you didnt make the turn, you ended up dropping 12 feet into a ravine? Well I ended up dropping 12 feet into a ravine, luckily the ground was very very mushy mud, and I broke the fall with my face. About 3 feet from where my face landed was a very hard and imposing rock, I believe the rock moved out of the way in fear for its own safety.

Every one thought I was dead, I could tell cause I heard my friend yell "OMG PATS DEAD!" Jokes on them I thought, You wont get rid of me that easy! So I passed my bike to a friend who had to half climb down to grab the front wheel. No permanent damage that I can remember, wait what i was talking about?