As Erin says they are very directional - almost like a laser beam. Also they tend to emit light quite near to infra red wavelengths so can be far more sensitive to things like ccd cameras etc than the human eye.
Some nifty brightness calculators and info here.
I have noticed that my LED torches will barely illuminate the surface of the sea due to the wavelength of the light.
Of course main advantages of LEDs are low battery consumption and very long life(100,000hrs).
Has anyone noticed the LED catseyes down Plymouth/Portsmouth way???