I've only seen waves that big at Jaws off the coast of Maui. Professional surfers have died there in 60+ foot waves.
A lot of the danger on those big waves is that when the swell from the shoreline retracts out past the reef, the ocean floor in front of the wave is sometimes only a few feet deep. You can get impaled on whatever reef is just beneath by all that water weight. Really makes you appreciate the power of the ocean. And I keep my ass off the big waves. :cool