We've all had a crash at one time or another. Mine have thus far (knock on wood) all come while riding modern, supposedly more reliable bikes. When I was maybe 8 or so I was riding on my lawn on a Schwinn (Aerostar I think it was). I hit a big, hidden hole, and the front wheel did a 90 degree turn to the right, driving the handlebars into my stomach. The force was enough that the bars came through the handgrips and left a big bruise.
I collected myself and went inside and hung around. I used the restroom and went upstairs. I thought it a bit strange that I was peeing red, but went upstairs to bed anyway. A little while later I was roused and my parents made a big fuss and took me to the hospital. I struggled and didn't want to have blood drawn from my arms (afraid of needles), so they tied me down to a spine board of some kind and took it and ran a battery of other tests. Apparently I'd sustained internal injuries as a result of the accident, though they had healed up enough by all accounts by the time they ran the tests that night. They sent me home and I was fine after that. Ironically enough, the only damage to the bicycle was that the rim went out of true, the handgrip was busted and the handlebar was a bit bent. It goes to show you that sometimes you're lucky enough that a crash causing major damage to the bicycle doesn't do heavy injury. On the other hand you might have a crash that does only minor damage to the bicycle, but are unlucky enough to suffer palpable injury. I'd rather be straightening a tank or fenders than having blood drawn from me and tests done at the hospital.
The scariest incident I had though was on a Specialized Hard Rock a few years ago. It was brand new and supposedly all adjusted. I was headed uphill in Rosslyn towards the Metro station late on night. All of a sudden I felt the chain jump-- it headed right into the rear wheel, fouling everything up. At just that moment the bicycle struck the curb at a bad angle and I felt it start to catapult me. Unfortunately there was a plate glass store window only 3 feet away on the sidewalk. I was deathly afraid of going head first into that window with no helmet. Anyway just as I felt the bicycle launching me I jumped straight up off the pedals. I cleared the handlebars and flew forward with my feet under me. I landed hard on the balls of my feet and on my toes and took to big lurch-steps foward, stopping just in time to make gentle contact with the window. The bicycle flopped onto the sidewalk behind me. The bicycle sustained only minor damage in the end, but it was one of those accidents that nearly puts you out of commission for a long time.
So I guess in the end, the truest measure of a "bad" accident is how you come out. I'd rather be in the shop fixing the bicycle than in the hospital wrecked.