I've ridden clipless for years and have never fallen. Started out with Shimano clipless SPD's on my mountainbike and now use Shimano SPD road pedals and have never fallen as a result of my pedals. I've crashed my mountainbike lots of times unfortunately for other reasons (endo over a dirt ramp, branch in the spokes on trail, etc.) but none of those had anything to do with pedals.

I have to agree with UMD, falling isn't a foregone conclusion when it comes to clipless pedals. In fact, falling over into some of the streets on which I ride could be fatal. My nightly weekday 20 mile ride is usually during heavy traffic time and I'd hate to fall over in front of an oncoming car. If you are just starting out, practice on your street a couple times or in a parking lot getting in and out of the pedals and pay attention when you ride. This isn't rocket science but you can hurt yourself or someone else if you make a stupid mistake in traffic. If your pedals are working properly, you should be able to get in and out without much of a problem.

My biggest hurdle was getting used to one sided road pedals. My MTB pedals can be clipped in on both sides. IMO, that's the only hassle with Shimano road pedals (no a problem with speedplay or crank bros at least).