My girlfriend almost got hit by a car yesterday, and a friend of hers actually did get hit, in separate incidents. Both were a result of a "left hook": a motorist turning left across the road at full speed through a gap in automotive traffic, without seeing a cyclist.
Motorists: Always signal and slow when turning left (or at all). Double check for pedestrian and bicycle traffic, and make sure you have an all clear before proceeding.
Cyclists: It is nearly impossible to guess that a car will turn left across the lane, even with good visibility. This seems to happen most when there is a 5-second gap between you and the end of a wave of motor traffic. If this ever happens, make sure to write down the make/model/color/license plate of the car, and report them as a drunk driver (they very well might be).