Flashing lights get noticed more than steady beams, as others have observed. What hasn't been mentioned is that front lights are even more important than rear lights.

Being rear-ended by another vehicle, though devastating, is quite rare. Last I looked it accounted for only about 3% of cycling fatalities. Being hit from the front, by vehicles turning across your lane, or pulling out in front of you at an intersection, is far more common. So having a flashing light at the front makes even more sense than having one at the rear.