In the 10 years i've been riding clipless, my first fall was the first time I ever tried them, as I was trying to pull the back wheel up before hitting a curb, I pulled too hard and went over the bars (on a mountain bike with Time ATAC Carbon pedals circa 1999). The second and last time I fell due to clipless pedals happened at the end of a wide radius turn to a stop, I clipped out my left foot which was on the inside of the arc and fell the opposite direction flat on my back. This happened in a pair of Crank Brother Quattro pedals.