My bike only has a coaster brake. I've had many close calls that's why I'm installing a front disc brake. My latest was on our Santa Cruz ride. We were flying at full throttle for a 1/2 mile and when I decided to let off the throttle, my throttle stuck at full throttle. Then was I was trying to slow the motor down by braking. My coaster brake arm's bracket snapped and the pedal almost kicked me off the bike. I evenually got the bike under control and haven't rode it since.
But I am in the works of upgrading my braking system!