Had a couple of those "oops, new at the clipless pedal thing & forgot to clip out" experiences when I first switched over.

Also, about a year ago, while on a training ride for the MS150, had another rider fall on top of me at a stop sign while I was stopped & my foot was on the ground. This person decided to "try clipless pedals" for the first time - the weekend before the ride - & forgot to unclip! I had a few bruises but was okay other than the softball sized lump on the inside of my thigh which had gotten caught between her & the frame of my bike. Took about 3 months for that to completely heal though ... not pretty!!!