I had a pretty nasty crash turning onto a road where there's lots of traffic and they go fast as well. Was pretty lucky not to get hit. It actually happened on my 27-speed MTB Desinged for suspension+ridden with rigid fork= crazy low BB. The bike was new and I dug the pedal in so hard the rear wheel lifted up 4-5 inches. The bike was fine, and so was I, except that I respect tight corners more since then.
No such mishap on my ss/fix conversion so far.