Originally Posted by coffeehaus

I use Specialized mountain shoes, which do have tread so that you don't walk on the cleat. The clip-less on the pedal has a spring that holds the front edge of the binding up to catch the cleat when you clip in. If you step on them with regular shoes, the binding rotates down to give you a level pedal. I've ridden in flip-flops with no less ease than on a regular platform. I haven't had any problems with getting them to release or having them release early. There are two types of Shimano SPD cleats, regular and multi-release. Multi-release will let go if you pull them hard, so they might be an option to keep in mind if you're worried about needing to get out of the bindings fast.