I seldom change lenses since I prefer to shoot with a pair of cameras and I am willing to carry the extra weight of the second body. One of my reasons for not liking to change lenses is possible damage to the lens by dropping it. However I never, even in my wildest imagination, thought about this extent of damage from dropping a lens. It is lucky no one was standing under it...
http://www.petapixel.com/2011/09/15/...-hole-in-roof/