I had an interesting experience coming home from work yesterday.
I was stopping on the highway, prior to making a left hand turn onto an intersecting road. As I pulled up behind a limo which was also stopped waiting, I unclipped from the left pedal, and while attempting to unclip the right, the bike of course went in that direction, and I couldn't get unclipped. As I fell over a semi went whizzing by in the next lane. I could feel the rush of air as it went by, I don't know how close.
When I got up again and rode off, I couldn't clip in again on the right pedal at all. I checked the cleat on that shoe and discovered one of the screws had come out. When I attempted to unclip, the cleat just twisted in the pedal and stayed put.
Another lesson learned. My shoes were the last thing I thought about checking before a ride, but I will from now on!