Allen Johnson crashed (if you can call it that). He hit a few hurdles in the beginning, then regained his balance, and finally hit two more and went down (his momentum made him dive under one, and finally he stopped flat on his stomach on the track).
Oh man, that totally SUCKS! 
Who had the best hurdles crash - Allen Johnson or Perdita Felicien? Would be curious to see how the Olympic judges would call that one!