Tom makes an excellent point about balance. I like clipless, and part of that is that I'm not afraid of the low speed tip-over, since my balance is good. My balance got good partly with practice on platforms, trying to not put a foot down for as long as possible. Eventually I started working on my trackstands, also with platforms. Now, I'm no trackstand pro, but I usually don't even unclip unless I'm stopped for more than a few seconds. Plus, it just seems like a really unlikely type of fall to cause serious injury. Much scarier to me is having my foot fly off the pedal... I've done that before; putting your foot into your spokes is a great way to get airborne.