Yep. I've bashed my heel on the front wheel of my Streetmachine on a several of occasions due to failure to clip in while giving it the beans uphill at a junction, which is merely painful. Obviously that's less of an issue with a trike, as you can just stay clipped in the whole time.
I've experienced the trike version once while pootling round the block in Inappropriate Shoes to test some fettle or other. No drama due to low speed, but it was enough to persuade me that it's worth going and getting some SPD shoes for, even if you just want to check the brakes aren't rubbing or whatever.
Always makes me cringe to see junior pedal car riders with the unholy combination of a) flat pedals b) 170mm cranks c) no floor. Fortunately they tend not to have a structural member in that position, and the weight:power ratio combined with cumulative frictional losses serve to limit the momentum involved. And they tend to be racing on half-decent tarmac and mashing in high gears, so less chance of losing a pedal in the first place.