I had several bad falls with first and second generation clipless from Look and Time. It was possible to pull out of these pedals on the upstroke, and the early attempts at including float in the systems (red Look cleats, for instance) were prone to disengaging on the down stroke. This resulted in unpleasantness when it occured during, say, a 1/pro field sprint. I am told that these problems have been solved, but early experiences put me off the whole business, so I went back to clips and straps and have rarely looked back. (I have Eggbeaters on my mountain bike, and can pull out of them on the upstroke.)

Properly set up clips and straps are extremely secure. This is a dying art, as there are few straps that work correctly -- and they are NOT inexpensive: a good pedal/strap setup can easily cost $250 -- and even fewer shoes with good cleats. Right now I am using Campagnolo laminated straps, Campy steel clips, and Campy Super Record pedals, none of which have been made in the last 15 years or so. I am also using an even older pair of ventilated leather shoes with wooden soles and extremely deep cleat slots. This is a reliable, comfortable setup which absolutely holds up to the most violent sprint, but can also be adjusted to allow the foot to be pulled out in an emergency. Too bad it can't do both at the same time.