I've toppled over more times from trying to switch chainrings while going up a steep hill and throwing my chain, but I've certainly fallen from clipless, too. One time I was riding to the grocery store and I just sort of forgot I'd just switched pedals, and I sort of almost hit a lady and rode my bike in through the automatic doors (luckily they opened for me) before I figured out what was up. Quite embarrassing and that lady was MAD and really, how do you explain Eggbeaters to a mad old lady?