I haven't fallen...yet.
I've heard many people say that you will inevitably fall soon after getting clipless. However, I was already used to pulling my shoe out of a toe basket, so the change wasn't major. Also, I set the tension fairly loose to start out with, so I could just "yank" in panic and unclip.
The closest I've ever come to falling has been on a couple of occasions when I was rolling to a stop, and had unclipped my right foot already (the one I always put down.) Something then caused me to lean to my left, and I was barely able to get that foot out.