bare-knuckle sucks.
risk of a broken bone in your hand is very, very real.. as is a broken or sprained wrist.
I'd done it before, but i'll never do it again w/o the money being worthwhile... I was always much, much tighter and controlled with my strikes than any of those guys.. just swinging wildly is a surefire way to break your hand or wrist. the damage to your face isn't even that bad, usually, as the majority of the strikes land on your skull (which sound like firecrackers in your ears w/o gloves).
the risk of a knockout is fairly low as well.. and usually only happens when you get tagged 'on the button' with a knuckle on your chin or behind the ear or rear of your jaw, which are all much, much harder to hit w/o gloves (which is why compact, boxing or karate-type strikes are more effective than the long, looping muay thai stuff.. muay thai punches, anyways.. not counting elbows)